Which of the following can terminate an offer?

Revocation and expiration of time are valid methods to terminate an offer in contract law. Revocation occurs when the offeror withdraws the offer before acceptance, and this can be communicated directly or can be implied through the offeror's actions. Expiration of time refers to the situation where an offer is only valid for a certain period; once that period lapses without acceptance, the offer automatically terminates.

While acceptance and counteroffers can impact an offer, they don't directly refer to termination in the same context. Acceptance signifies agreement, while a counteroffer negates the original offer and proposes new terms, rather than simply terminating the initial offer. Negotiation and discussion may lead to modifications or the creation of an agreement, but they do not necessarily terminate an offer unless they explicitly state the offer is being withdrawn. Documentation and formality typically relate to the requirements for creating or enforcing a contract but do not specifically address offer termination. Thus, revocation and expiration of time are the clear, straightforward methods by which an offer can be terminated.