Franz Bought a Round Trip Ticket to Germany to Visit

Franz bought a round trip ticket to Germany to visit relatives. Unfortunately, a week before flight time, he broke his leg. He offered his co-worker, Joe, the ticket for 80% of the full price, offer to remain open until 10:00 p.m. on December 15. Indicate to Joe which of the following is true with regard to the law of offer and acceptance.

A) If Franz sells to someone else, it is too late for Joe to accept the original offer.
B) A letter of acceptance is always effective when it is dropped in the mailbox.
C) If Joe makes a counteroffer of 50% of the full price, and Franz rejects the counteroffer, Joe can still accept the original offer.
D) To create a contract, an offer must be in writing.
E) Franz could revoke the offer anytime before acceptance, even before 10:00 p.m. on December 15.