衛(wèi)生類：完形填空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. __1__ these wide modern roads are generally __2__ and well maintained， with few sharp curves and __3__ straight sections， a direct route is not always the most __4__ one. Large highways often pass __5__ scenic areas and interesting small towns. Furthermore， these highways generally __6__ large urban centers which means that they become crowded with __7__ traffic during rush hours， __8__ the "fast， direct" way becomes a very slow route. However， there is almost always another route to __9__ if you are not in a hurry. Not for from the relatively new "superhighways"， there are often older， __10__ heavily traveled roads which go through the countryside. __11__ are good lane roads; others are uneven roads curving __12__ the country. These secondary routes may go up steep slopes， along hilly cliffs or down frightening hillsides to towns __13__ in deep valleys. Though these are less __14__ routes， longer and slower， they generally go to places __15__ 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.