【SC精选精讲36】In the mid-1920s

In the mid-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 

the effects (that changes in working conditions would have) on workers' performance  

技能get: the Intended Meaning, 定语从句省略that