The correct answer is A. Absolve.
To absolve someone is to declare them free from guilt or blame. It is the opposite of accuse.
To exonerate someone is to clear them of blame or suspicion. It is similar to absolve, but it is more specific in that it refers to clearing someone of a specific crime or accusation.
To vindicate someone is to prove them right or to justify their actions. It is similar to exonerate, but it is more general in that it can refer to any situation in which someone is accused or criticized.
To impeach someone is to charge them with a crime or misconduct, especially in a political context. It is the opposite of absolve, exonerate, and vindicate.
In conclusion, the correct answer is A. Absolve.