It’s difficult for the village children to cross the river to get to school.I thin

问题补充：

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

--- I think a bridge over the river.

A. should be built

B. should build

C. was built

D. has been built

答案：

(答案→)A. should be built

B. should build

C. was built

D. has been built

解析：句意：对于这个村的孩子们来说过河去上学很困难。——我认为应该在河上建一座桥。结合语境可知从句中描述的是对客观动作的虚拟，故用should虚拟语气，从句主语是动作对象，故用被动语态，选A。