Marilyn Read an Ad in the School Newspaper Offering a $1,000

Marilyn read an ad in the school newspaper offering a $1,000 swimming scholarship to anyone who could swim 500 laps in the school pool. Marilyn called the advertiser and began swimming. She has reached lap number 460; she feels great and is sure she can make it all the way. The advertiser:

A) may revoke the offer since there has not yet been an acceptance.
B) may not revoke the offer since Marilyn has already accepted it.
C) must permit Marilyn the opportunity to finish her attempt to swim the 500 laps, or pay damages if he interferes with the completion of the laps.
D) must pay Marilyn $920, because she has performed 92% of the offer.