prep一道题求解。

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

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