题目内容：
回答题：Highways in the United States
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. __51__ these wide modern roads are generally __52__ and well maintained, with few sharp curves and __53__ straight sections, a direct route is not always the most __54__ one. Large highways often pass __55__ scenic areas and interesting small towns. Furthermore, these highways generally __56__ large urban centers which means that they become crowded with __57__ traffic during rush hours, __58__ the "fast, direct" way becomes a very slow route. However, there is almost always another route to __59__ if you are not in a hurry. Not for from the relatively new "superhighways", there are often older, __60__ heavily traveled roads which go through the countryside. __61__ are good lane roads; others are uneven roads curving __62__ the country. These secondary routes may go up steep slopes, along hilly cliffs or down frightening hillsides to towns __63__ in deep valleys. Though these are less __64__ routes, longer and slower, they generally go to places __65__ the air is clean and the scenery is beautiful, and the driver may have a chance to get a fresh, clean view of the world.
A．Although
B．But
C．Since
D．Because.
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