The United States is well-known for its network of major highways designed to help a drive

r get from one place to another in the shortest possible time.【C1】______ these wide modem roads are generally【C2】______ and well maintained, with【C3】______ sharp curves and many straight【C4】______ , a direct route is not always the most【C5】______ one. Large highways often pass【C6】______ scenic areas and interesting small towns, Furthermore, 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 mute.

However, there is【C10】______ always another route to take【C11】______ you are not in a hurry. Not far from the 【C12】______ new "suqerhighways', there are often older, 【C13】______ heavily traveled roads which go through the countryside.【C14】______ of these are good two-lane roads; others are uneven roads【C15】______ through the country. These secondary routes may go up steep slopes, along high【C16】______ , or down frightening hillsides to towns【C17】______ in deep valleys, Through these less direct routes, longer and slower, they generally go to places【C18】______ the air is clean and the scenery is beautiful, and the driver may have a 【C19】______ to get a fresh, clean【C20】______ of the world.

【C1】

A．Although

B．Since

C．Because

D．Therefore