Judith, an Ill-Tempered Business Law Teacher, Offers $50 to Any

Judith, an ill-tempered business law teacher, offers $50 to any student who will mow her lawn. Peter goes right over and begins mowing. Just before he finishes, Judith goes over and tells him that she revokes her offer. Which of the following is true regarding Peter's entitlement to payment?

A) Peter is not entitled to payment because a bilateral contract was involved that could only be accepted by full performance prior to revocation.
B) Peter is not entitled to payment because a unilateral contract was involved that could only be accepted by full performance prior to revocation.
C) Peter is entitled to only a proportional recovery based on the amount of work he had done prior to the revocation because Judith always retained the right to validly revoke.
D) Peter is entitled to recover because a unilateral contract was involved, and he was entitled to a reasonable amount of time to complete the job.
E) Peter is entitled to recover because a bilateral contract was involved, and he was entitled to a reasonable amount of time to complete the job.