Select the correct passive form of the given sentence.
The Inspector had already proved the case before the investigation team took charge of it.

Options

A. The case was already proved by the Inspector before the investigation team took charge of it.
B. The case was already proved by the Inspector before the investigation team took charge of it.
C. The case had already been proved by the Inspector before the investigation team took charge of it.
D. The investigation team took charge of the case but the Inspector had already proved before it.

Explanation

(c) The case had already been proved by the Inspector before the investigation team took charge of it. (Correct) (a) The case was already proved by the Inspector before the investigation team took charge of it. (Tense has changed) (b) The case had already proved by the Inspector before the investigation team took charge of it. (Tense has changed) (d) The investigation team took charge of the case but the Inspector had already proved before it. (Incorrect Tense and Subject)