Rastis wrote: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

In A, it is unclear whether their refers to changes or to effects.
Eliminate A.

C: The Hawthorne Works WAS the scene...for investigating...what the effects...ARE.
Here, the sequence of events is illogical:
It is not possible that the Hawthorne Works WAS the scene (in the past) for investigating what the effects ARE (in the present).
Eliminate C.

D: changes in working conditions' effects
Here, there are changes in the EFFECTS.
The intended meaning of the original sentence is that there were changes in the WORKING CONDITIONS THEMSELVES.
Since D does not convey the intended meaning, eliminate D.

Generally, an infinitive modifier (to + VERB) serves to express the INTENT of the preceding SUBJECT.
John conducted an experiment to determine the difference in growth rates.
Here, to determine the difference in growth rates is attributed to John -- the preceding subject -- expressing John's INTENT when he conducted an experiment.
E: The Hawthorne Works was the scene of an intensive series of experiments to investigate.
Here, to investigate does not serve to express the intent of the Hawthorne works (the preceding subject).
Eliminate E.

The correct answer is B.