你可能感兴趣的试题

Earthquake and Animals
Scientists who try to predict earthquakes have gotten some new helpers recently —animals.Animals often seem to know in advance that an earthquake is coming，and they show their fear by acting in strange ways.Before a quake 地震）in China in 1975snakes awoke from their winter sleep early only to freeze to death in the cold air.All the unusual behavior，as well as physical changes in earth，alerted （提醒）Chinese scientists to the coming quake.They moved people aw/ay from the danger zone and saved thousands of lives.，
One task for scientists today is to learn exactly which types of animal behavior.predict quakes.It is not an easy job.First of all not every animal reacts to the danger of an earthquake.Just before a California quake in 1979，for example，an Arabian horse became very nervous and tries to break out of his stall.The horse next to him，however，remained perfectly calm.It is also difficult sometimes to tell the difference between normal animal cahnness and ’earthquake nerves’.A zookeeper once told earthquake researchers that his cougar （美洲狮）had been acting strangely.It turned out that the cougar had a stomachache.
A second task for scientists is to find out.exactly what kinds of warning the animals receive.They know that animals sense far more of the world than humans do.Many animals can see，hear，and smell things that people do not even notice.Some can detect tiny changes in air pressure，gravity，or the magnetism （磁力）of earth.This extra sense probably helps animals predict earthquakes.
A good example of this occurred with a group of dogs.They were closed in an area that was being shaken by a series of tiny earthquakes.Before each quake a low boomingsound was heard.Each sound caused the dog to bark （吠）wildly.The dogs began to bark during a silent period!A scientist who was recording the quakes looked at his machine.He realized that the dogs had reacted to a booming noise.They also sensed the tiny quake that followed it.The machine recorded both，though humans felt and heard nothing.
In this case there was a machine to check what the dogs were sensing.Many times，however，our machines record nothing out of the ordinary，even though animals know a quake is coming.The animals might be sensing something we do measure but do not recognize as a warning.Discovering
what animals sense，and learning how they know danger signals，is a job for future.