On January 1, Esau sent an offer by mail to Jacob offering to sell Esau's birthright to Jacob in exchange for a bowl of stew. On January 7, Esau reconsidered and sent Jacob a letter of revocation. On January 5, Jacob received Esau's offer letter and immediately sent a letter of acceptance. On January 10, Esau received Jacob's acceptance letter. On January 12, Jacob received Esau's revocation letter. When was the contract formed?

a. Never, the offer was rescinded

b. January 1

c. January 5

d. January 10