Regarding contractual offers, which of the following statements is true of a unilateral offer?
1) Silence from the offeree can be construed as acceptance.
2) The offeror cannot revoke the offer until the offeree has had an opportunity to respond to the offer.
3) The offeror must give the offeree a reasonable time to complete it if the offeree has begun performing.
4) The offeror can rescind it at any time.