A homeowner tells a contractor, 'I'll pay you $1,000 if and when you finish removing the fallen tree,' and the contractor completes the removal. This is an example of acceptance of:

Giải thích

An offer that asks for a completed act rather than a return promise is a unilateral contract offer, and performance of the act is both the acceptance and the performance (Civil Code §1584) — finishing the removal obligates the homeowner to pay. (b) is the standard confusion: had the homeowner said 'promise me you will remove it and I will pay $1,000', the exchange of promises would make it bilateral. (c) misapplies Civil Code §1624, which reaches contracts not performable within a year, transfers of real property and the like, not a same-day tree removal. (d) misreads 'if and when you finish' as reserving a choice; it states a condition on the contractor's performance, not an escape from the homeowner's promise, so the promise is not illusory.