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
问题描述：
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
B have been put in
LABOR可以看成是一个集体名词。。。所以用HAVE不用HAS。。
前面是REQUIRES。也就是一般时态。。所以后面也要用一般时态。。。
MORE表示要做比较，比之前多。。那就是要比较已完成的事情。。所以用现在分词。。。。
答
A has been put in
应该用过去时
C表示正在进行 D表示将来
而B用了复数
劳动力是单数
答
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
答
A 省略了后面的主语project 比之前的劳动力还多
所以..