【单选题】

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.

Although these wide modem roads are generally (21) and well maintained, with few sharp curves and straight sections, a direct route is not always the most (22) one. Large highways often pass (23) scenic areas and interesting small towns. Furthermore, these highways generally (24) large urban centers, which means that they become crowded with heavy traffic during rush hours, (25) the" fast, direct" route becomes a very slow route.
However,there is almost always another route to take if you are not in a hurry. Not far from the (26) new" superhighways", there are often older, (27) heavily traveled roads which go through the countrvside. (28) of these are good two-lane roads ; others are uneven roads curving through the country. These secondary routes may go up steep slopes, along high cliffs, or down frightening hillside to towns (29) in deep valleys. Through these less direct routes, longer and slower, they generally go to places (30) the air is clean and scenery is beautiful, and the driver may have a chance to get a fresh, clean view of the worlD、
A．stable
B．splendid
C．smooth
D．complicated