介词歧义？？！！

shiwen66666

这是原题：
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
选B
请问C：for 什么时候会对？是指由表因为和固定搭配对，其他必错吗？请NN指正