Answer:
d. Gavin is allowed to revoke if he finds Rod's efforts half-hearted
Step-by-step explanation:
Either he accepts, or he does not accept the offer. Even if he started to paint without accepting the offer, and Gavin does not like his work, the offer can be revoked.
So the correct answer is:
d. Gavin is allowed to revoke if he finds Rod's efforts half-hearted