On Thursday, Angie decided to accept Harry's counteroffer for the purchase of his house. She signed the counteroffer and placed it in the mail. On Friday, Harry decided that he had asked too low a price for the house, so he faxed Angie stating that the counteroffer was withdrawn. On Saturday, Harry received Angie's acceptance in the mail. Under the mailbox rule, which of the following is true?

a. Harry withdrew his offer, so no contract was formed

b. Harry did not withdraw his counteroffer in time, so a contract was formed

c. Harry may not make a counteroffer

d. Harry's withdrawal was ineffective since it was not in writing