GMAT Sentence Correction (SC) | A group of FBI investigators, in connection with the 1975

Logically we are aware that if a modifier when removed disturbs the meaning of the intended clause, then it turns an essential modifier and should not be encased between commas. Choices A through D have non-essential modifier intercepting the clause between the subject and the verb. When the parenthetical element is masked, you find the sentences missing the original intent. Therefore, the modification is defective in all these four choices. This leaves us with only E, which has no such blatant
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