We collected a lot of books to get the necessary information but only half helpful so we

问题补充：

We collected a lot of books to get the necessary information but only half helpful, so we failed to finish the work.

A. is

B. are

C. was

D. were

答案：

A. is

B. are

C. was

(答案→)D. were

解析： 考查主谓一致.句意:我收集了许多书以获得必要的信息,但是只有一半有帮助,因此我们未能按时完成工作.根据上下文可知谓语动词用过去时态,复数的一半还是复数,故用are的过去时态were,选D.