On May 1, Owner orally offered to pay Alex $15,000 if Alex would repair the roof on Owner's beach cottage. Alex requested some time to think it over. Owner told Alex she could have a couple of days to think about it, but that he had to know Alex's decision no later than May 4. On May 3, Alex sent a properly addressed e-mail to Owner, accepting the offer. She started working on the roof on May 4. If Owner's offer to Alex is considered an offer unambiguously looking for a unilateral contract, which of the following is true?
(A) Alex had to notify Owner of her acceptance before she started repairing the roof, otherwise her acceptance was ineffective.
(B) Alex's dispatch of the e-mail on May 3 was a valid acceptance of Owner's offer.
(C) Alex may cease, without breach, if she has started to perform; but Owner must hold his offer open for a reasonable period of time.
(D) Alex would be in breach if she walked off the job before completion.