实在看不明白，请高手帮忙指点，谢谢！

PREP语法172题版

157. In the mod-1920s 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 the effects on workers’ performance are that changes in working conditions would cause

D.  that investigated changes in working conditions’ effects on workers’ performance

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

这里为什么是was?前面是个整体？这句话看不明白。为什么选B？其他选项又有什么问题？

语法真的不过关，烦请高手指点，在此谢过 ~

investigate的宾语是effects,effects后面接的是定语从句，其中that做从句里面的宾语，changes是主语，have是谓语，你把on workers’ performance先省略掉来读句子就比较清楚了