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.

60().

A.reduce 

B.permit 

C.recruit 

D.limit

蛛网膜下隙出血的病因有哪些?