The United States is well-known for its network of major highways de signed to help a driver get from one place to another in the shortest possible time.【C1】______ these wide modern roads are generally【C2】______ and well maintained, with【C3】______ sharp curves and straight sections, a direct route is not always the most【C4】______ one. Large highways often pass 【C5】______ scenic areas and interesting small towns.【C6】______ , these highways generally【C7】______ large urban centers, Which means that they become crowded with【C8】______ traffic during rush hours,【C9】______ the "fast, direct" route becomes a very slow route.
However, there is almost always another route to take【C10】______ you are not in a hurry. Not far from the【C11】 ______ new" superhighways", there are often older,【C12】______ heavily traveled roads which go through the 【C13】______ .【C14】______ of these are good two lane roads; others are【C15】______ roads curving through the country. These secondary routes may go up【C16】______ slope, along high【C17】______ , or down【C18】______ hillside to towns 【C19】______ in deep valleys. Through these less direct routes, longer and slower, they generally go to places【C20】______ the air is clean and scenery is beautiful, and the driver may have a chance to get a fresh, clean view of the world.
【C1】

Although
B. Since
C. Because
D. Therefore