问题补充:
The number of private cars in urban areas should be limited the number of public buses should be increased.
A. when
B. while
C. unless
D. until
答案:
A. when
(答案→)B. while
C. unless
D. until
解析:考查连词:A. when当…时候B. while 当…时候,然而C. unless除非D. until直到,句意:都市的私家车数量应该减少而公共汽车的数量应该增加。选B。