The correct answer is C. His Cabinet had already been informed about his decision by the Minister.
The sentence “The Minister had already informed his Cabinet about his decision” is in the past perfect tense. This tense is used to talk about something that happened before another event in the past. In this case, the Minister informed his Cabinet about his decision before the time that is being talked about.
The other options are not in the past perfect tense. Option A, “His Cabinet was already informed about the Minister’s decision,” is in the simple past tense. This tense is used to talk about something that happened at a specific time in the past. Option B, “His Cabinet has already informed the Minister about his decisions,” is in the present perfect tense. This tense is used to talk about something that happened at some point in the past and continues to be true in the present. Option D, “His Cabinet will have already been informed about the Minister’s decision,” is in the future perfect tense. This tense is used to talk about something that will happen before another event in the future.
In conclusion, the correct answer is C. His Cabinet had already been informed about his decision by the Minister.