On March 1, Hotz Apartments, Inc., received from Koolair, Inc., a letter offering to sell Hotz 1,200 window air conditioners suitable for the apartments in Hotz's buildings. The Koolair offer stated that it would remain open until March 20, but that Hotz's acceptance must be received on or before that date. On March 16, Hotz posted a letter of acceptance. On March 17, Koolair telegraphed Hotz to advise that it was revoking the offer. The telegram reached Hotz on March 17, but Hotz's letter did not arrive at Koolair's address until March 21. As of March 22, which of the following is a correct statement? 
The telegram revoking the offer was effective upon receipt. The offer was revocable at any time for lack of consideration. The mail was the only authorized means of revocation. Under the terms of Koolair's offer, Hotz's attempted acceptance was ineffective. 