Increasingly, the development of tourism is seen to have an effect on the environment. Erosion (磨损) is one problem. The steps and stones of major popular (51) like Shakespeare’s birthplace or Stonehenge (巨石阵) are literally being worn away by millions of foreign feet. The (52) in the case of Britain’s best known prehistoric monument has been to use railings to keep visitors at a distance. Such measures can hardly be (53) in the house of the Bard, however, where tourists want to enter the actual building.

Overcrowding in cities, towns and villages is (54) problem. Traffic jams are an outcome. In narrow roads, tourist vehicles cause congestion. (55) traders and residents cannot get around to do their work. Car parks fill up, (56) strangers park their cars where they can: in streets, across gateways, in lay-bys, or even in (57) driveways. This causes obstruction. The sheer weights of in-comers can be a hazard. Thus Venice, a city built for half a million inhabitants, is (58) by another half million who populate the city daily in the tourist (59) —eight million visits each year. The mayor recently decided to (60) visitors to 90,000 a day. the only way to save the city from overcrowding.

55().

A.Urban 

B.Local 

C.Rural 

D.Foreign

每题给你一个数列，但其中缺少一项，要求你仔细观察数列的排列规律综合判断，然后从四个供选择的选项中选出最恰当的一项，来填补空缺项。

18，20，23，25，27，28，28，( )。

A．36

B．32

C．26

D．21