GMAT Sentence Correction (SC) | Hawthorne Works

In the mid-1920’s the Hawthorne Works of the Western Electric Company was the scene of an intensive series of experimentsthat 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 are the effects in workers’ performance that
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