单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.

单项选择题

The tower of Pisa has been leaning so long—nearly 840 years—that it"s natural to assume it will 1 gravity forever. But the famous structure has been in danger of collapsing almost since its first brick was 2 .
It began leaning shortly after construction began in 1173. Builders had only reached the third of the tower"s 3 eight stories when its foundation began to settle unevenly on soft soil composed 4 mud, sand and clay. As a result, the structure leaned 5 to the north. Laborers tried to 6 it by making the columns and arches of the third story on the sinking northern side slightly taller. Then political unrest halted construction.
The tower sat 7 for nearly 100 years, but it wasn"t done moving. By the time work restarted in 1272, the tower tilted to the south—the 8 it still leans today. Engineers tried to make another 9 , only to have their work interrupted once again in 1278 with just seven stories completed.
Unfortunately, the building continued to settle, sometimes at an 10 rate. Finally, between 1360 and 1370, workers finished the project, once again trying to correct the lean 11 angling the eighth story, with its bell room, northward.
In 1989, a similarly constructed bell tower in Pavia, Italy, collapsed suddenly. Officials became 12 worried the tower of Pisa would suffer a similar fate that they closed the monument to the 13 . A year later, they rallied together an international team to see 14 the tower could be brought back from the brink.
By 2001, the team had decreased the tower"s lean by 44 centimeters, enough to make officials 15 that they could reopen the monument. The actions taken by Burland and his team could, 16 , stabilize the structure forever. The real threat now comes from the masonry itself, especially the material in the 17 stories, where most of the forces caused by the centuries-long leaning have been directed. If any of this masonry crush, the tower could collapse. And even a 18 earthquake in the region could have devastating consequences.
After 200 years, another intervention may be required, but the 19 available to make improvements could be far more advanced and 20 the tower for another 800 years.