The project requires more labor than ___ because it is extremely difficult.

题目

The project requires more labor than ___ because it is extremely difficult.
A has been put in B have been put in C being put in
D to be put in

答案

A
句意为:这项工程要求(比现在)更多的人力,因为它极其困难.
可见时态为现在完成时,排除C(进行时)和D(将来时)
labor不可数名词,谓语用单数,排除B