D is the best answer. Real-estate contingencies should normally contain clear, definite deadlines. Examples include financing contingencies, home-inspection contingencies, condominium-document review periods, and other conditions that depend partly on third-party activity.

The reason is contractual certainty. If a contingency remains open indefinitely, neither buyer nor seller knows when the transaction becomes firm or when either party may exercise rights related to the contingency. A defined period forces the party benefiting from the contingency to act diligently and establishes when the condition must be satisfied, waived, or invoked.

“Reasonably short” does not mean unreasonably restrictive. The deadline must provide sufficient time for the relevant lender, inspector, attorney, condominium association, or other party to perform the required function.

Massachusetts Board contract curriculum specifically identifies contingencies and “time is of the essence” concepts as important purchase-contract provisions.

The exact deadline is a matter of contract terms rather than a universal statutory number.

Study Guide Reference: Contracts — contingencies, deadlines, financing and inspection provisions.