第二节 完型填空
阅读下面短文，从短文后所给各题的四个选项(A、B、C和D)中选出能填入相应空白处的最佳选项。
The United States is well-known for its network of major highways designed to help a driver get from one place to another in the shortest possible time. 【B1】 these wide modern roads are generally 【B2】 and well maintained (维护), with 【B3】 sharp turns and many straight 【B4】 , a direct route(路线) is not always the most 【B5】 one.
Large highways often pass 【B6】 scenic areas and interesting small towns. Furthermore, these highways generally 【B7】 large urban center which means that they become crowded with 【B8】 traffic during rush hours, 【B9】 the 'fast, direct' way becomes a very slow route. However, there is 【B10】 always another route to take 【B11】 you are not in a hurry. Not far from the 【B12】 new 'superhighways' ,there are often older, 【B13】 heavily traveled roads which go through the country side. 【B14】 of these are good two lane roads; others are uneven roads 【B15】 through the country.
These secondary 【B16】 may go up steep slopes, along hilly cliffs (悬崖)or down frightening hillsides to towns 【B17】 in deep valleys. Though these are less direct routes, longer and slower, they generally go to places 【B18】 the air is clear and the scenery is beautiful, and the driver may have a 【B19】 to get a fresh, clean 【B20】 of the world.
【B1】
A．Although
B．Since
C．Because
D．Therefore