Franz Bought Two Front-Row Tickets to a Sold-Out Concert

Franz bought two front-row tickets to a sold-out concert.Unfortunately,a week before the concert,he found out he had to go on a business trip and would miss the concert.He offered his co-worker,Joe,the tickets 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 counter-offer of 50% of the full price,and Franz rejects the counter-offer,Joe can still accept the original offer.
D) Franz could revoke the offer at any time before acceptance,even before 10:00 p.m.on December 15.
E) To create a contract,an offer must be in writing.