Final answer:
a) Mirror image rule
The term that describes the principle where an acceptance must exactly match the terms of the offer is known as the mirror image rule.
Step-by-step explanation:
An acceptance must indeed exactly match the terms of the offer in order to be valid. This principle is known as the mirror image rule. It holds that for an acceptance to create a binding contract, the acceptance must be an unequivocal statement that the offeree accepts the terms of the offer exactly as they are presented, without variations or qualifications. If the offeree changes the terms or adds new ones, it is not an acceptance but rather a counteroffer, which the original offeror can choose to accept or reject. The mirror image rule is a traditional common law principle, although it has been modified by statutes such as the Uniform Commercial Code (UCC) in commercial transactions involving the sale of goods.