Sam tells his accountant, "I must have this year's audit completed by March 1." The accountant agrees to complete the audit by March 1. Under general contract law, if the audit is not completed by March 1, does Sam not have to pay the accountant for the audit?

a. Yes, he has to pay if the agreement is in writing.
b. No, he doesn't have to pay if there is a breach.
c. No, he doesn't have to pay until the audit is done.
d. Yes, he has to pay if he signed the contract.