One of the most convenient and cheapest ways to see America is by riding a Greyhound bus. This interstate bus system connects all major cities in the United States, (52) people with frequent and convenient service. The bus system even has an international service (53) makes connection with cities in Canada and Mexico.
Its network even extends to some of the smaller towns and out-of-the-way communities (54) the great interior of the country. Traveling by bus may (55) longer than flying by plane, but the terminals are located in the center of most cities and there is (56) to the downtown area. These buses are comfortable and air-conditioned. They are all equipped with toilets in the rear to (57) the convenience of the passengers, but there are some very severe (58) of conduct which are strictly enforced. On all buses (59) is forbidden and the consumption of alcoholic drinks is not allowed.
(60) bus travel may not be suited to everyone’s taste, it affords budget travelers the (61) to see America in comfort and safety and at a leisurely unhurried pace.
57().
A. keep up
B. result in
C. add to
D. look after
参考答案：C
解析：
此题考查的是对四个选项的理解。look after一般是在人作主语的时候使用，而题中的they是指bus。result in意思是“导致后果”’一般用作贬义。Keep up意思是“维持状态，继续做某事”。只有add to和题目相符。
