Which of the following is true about the mailbox rule?
O To be valid, every acceptance must be mailed via the US Post Office to the offeror.
O Acceptance must match the terms of the offer exactly in order to be valid.
O An offer can be revoked after an offeree has mailed the acceptance to the offeror.
O Once an acceptance is sent or otherwise communicated to the offeror by an authorized means, the acceptance is effective.