Concept:A valid contract is formed when one party makes a clear offer and the other party gives a definite acceptance of that offer.
Explanation:Offer and acceptance are the foundational elements on which every valid contract is built.
An offer is a proposal made by one party indicating that something of value is available for exchange.
Acceptance occurs when the other party agrees to that proposal without changing its terms.
Other options like discharge, performance, age, and promise describe later stages or certain requirements of a contract, not the essential elements needed to form one.
Therefore, the correct pair is offer and acceptance.
Answer:B. Offer and acceptance