Select the correct passive form of the given sentence.

The Inspector had already proved the case before the investigation team took charge of it.

The case had already been proved by the Inspector before the investigation team took charge of it.

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

The original sentence is in the Active voice, with the subject "Inspector" performing the action of "proving" the case. The passive voice of the sentence would have the case as the subject, and the action of "being proved" would be performed on it. The correct passive voice form of the sentence would be "The case had already been proved by the Inspector before the investigation team took charge of it."

The other options are incorrect. The case was already proved by the Inspector before the investigation team took charge of it is also a correct passive form of the sentence, but it is not the most grammatically correct form. The use of the verb "was" instead of "had" implies that the action of proving the case happened in the past and continues to have an effect in the present. However, the sentence does not indicate that the case is still proved.

The case had already proved by the Inspector before the investigation team took charge of it is grammatically incorrect because the verb "proved" is in the wrong form. The correct form of the verb "prove" for the passive voice of this sentence would be "be proved."

The investigation team took charge of the case but the Inspector had already proved before it is in the active voice, but the word order is incorrect. The correct word order for the active voice is "subject + verb + object."