As part of an advertising campaign, a plane flew over the beach in Ocean City trailing a banner that read: "Boardwalk Bistro will give $100 to the first person to swim from the inlet at 1st Street to Bistro's at 33rd street." Daisy was a very strong swimmer and accepted the challenge. When she got to 25th Street, however, the plane appeared again with a banner that read: "Bistro withdraws its offer." Which statement best describes Daisy's and Bistro's rights in this situation?

a. Bistro may revoke the offer because there it will not be accepted until Daisy reaches 33rd Street.
b. Bistro can revoke the offer because Daisy did not notify Bistro that she intended to accept the offer.
c. Bistro cannot revoke the offer because this is a bilateral contract.
d. Bistro cannot revoke the offer because Daisy has substantially performed the requested action.

Ans: d. Bistro cannot revoke the offer because Daisy has substantially performed the requested action.