By the time my neighbor got home, the police ___ left.

• A. Had already
• B. Have already
• C. Has already
• D. Having already

Answer: (A)

When two past events are in play, and one happens before the other, we use the past perfect for the earlier action, especially with phrases like “by the time.” Here, the neighbor’s return happened after the police left, so the leaving is the earlier event. Saying “the police had already left” shows that the police’s departure was completed before the neighbor got home, and the word “already” emphasizes that completion.

Other forms don’t fit the timing: present perfect (“have already left”) connects to now rather than to that past moment; “has already left” mismatches the plural subject “the police”; “having already left” doesn’t work grammatically in this sentence; and simply using “left” wouldn’t convey the sequence.