Final answer:
In the context of contract law, Chris's original offer to sell her printer can be terminated by her death, the sale of the printer to someone else, revocation of the offer, or the passage of the offer's expiration date. A counter-offer by an offeree would also terminate the original offer.
Step-by-step explanation:
The question pertains to contract law and the termination of an offer. In contract law, a valid offer can be terminated in several ways. An offer can be terminated by the action of the parties or by operation of law. Chris's death before acceptance and the sale of the printer to her brother before acceptance would both terminate the offer by operation of law and by the action of the parties, respectively. A revocation of the offer by Chris before acceptance would also terminate the offer, as the offeror is allowed to revoke the offer before it's been accepted. However, if the offer reaches its specified expiration at noon on February 20 without any acceptance, it would naturally come to an end. Lastly, a counter-offer by an offeree is seen as a rejection of the initial offer and replaces it with a new offer, thereby terminating the original offer. Therefore, all options provided, except for the counter-offer, would not terminate Chris's original offer to her classmate.