On May 1 Ralph offers to harvest Sams corn crop, and promises to keep the offer open until June 1. On May 3 Ralph mails Sam a letter revoking the offer. Sam receives the letter on May 5 and responds on May 6. Ralphs revocation of the offer became effective on:

a) May 3

b) May 5

c) May 6

d) no date because the offer is irrevocable

c)

d)