How does an offer differ from an option contract?

A. an offer has to be communicated before it can be accepted, but an option contract does not have to be communicated

B. an offer must contain definite terms, but an option contract is simply an outline of a proposed agreement

C. an offer can be revoked by the offeror at any time before the offeree accepts the offer, but an option contract has expired

D. an offer is valid until it is rejected by the offeree, but an option contract ends at the option of the offeror