请教大全补充-066（看了以前的贴子还是不明白）

66.   In the mid-1920’s the Hawthorne Works of the Western Electric Company was the scene of an intensive series of experiments that would investigate changes in working conditions as to their effects on workers’ performance.

(A) that would investigate changes in working conditions as to their effects on workers’ performance

(B) investigating the effects that changes in working conditions would have on workers’ performance  

(C) for investigating what are the effects in workers’ performance that changes in working conditions would cause

(D) that investigated changes in working conditions’ effects on workers’ performance（B）

(E) to investigate what the effects changes in working conditions would have on workers’ performance

这道题看的我一头雾水，主要是不了解逻辑意思，哪位nn能帮忙解释一下？