-It's difficult for the village children to cross the river for school.

- I think a bridge _________ over the river.    [ ]

A. was built    

B. is being built  

C. should be built  

D. has been built

国民生命表与保险公司使用的经验生命表相比起死亡率（）。

A.较高

B.较低

C.相同

D.时高时低