On May 1 Meat Company Offers to Cure and Smoke

On May 1 Meat Company offers to cure and smoke Natural Farm's products, and promises to keep the offer open until June 1. On May 3 Meat mails Natural a letter revoking the offer. The farm receives the letter on May 5 and responds on May 6. The company's revocation of the offer became effective on

A) May 3.
B) May 5.
C) May 6.
D) no date because the offer is irrevocable.