Directions: For each blank in the following passage, there are four choices marked A, B, C and D. Choose the one that is most suitable and mark your answer by blackening the corresponding letter on the Answer Sheet.
Without proper planning, tourism can cause problems. For example, (21) many tourists can (22) public places that are also enjoyed (23) the inhabitants(居住者) of a coun- try: If tourists (24) too much traffic, the inhabitants become annoyed and (25) . They begin to dislike tourists and to (26) them impolitely. They (27) how much tourism can help the country's economy. It is important to (28) about the people of a tourist attraction and how tourism affects it. Tourism should help a country (29) the customs and beauty that attract tourists.
Too much tourism can be a problem. If tourism (30) too quickly, people must leave other jobs to work in the tourism industry. This (31) that other parts of the country's economy can suffer.
On the other hand, if there is not enough tourism, people can (32) jobs. Business can also lose money. It (33) a great deal of money to build large hotels, airports, air terminal, first class roads, and other support facilities(设施) (34) by tourist attractions. For example, a major international-class tourism (35) can cost as much as 50 thousand dollars per room to build. If this room is not used most of the time, the owners of the hotel lose money.

21.