Unilateral Contract:.
A) Contract agreed to orally or in writing.
B) Contract in which both parties make promises to perform; a promise is given in return for another's promise.
C) A contract that arises from circumstances and is not expressed verbally or in writing by the parties.
D) Contract in which one party promises to perform in exchange for the performance of the other party.

Contract in which one party promises to perform in exchange for the performance of the other party.

Explanation:

A unilateral contract is any agreement in which the offeror in agreement is liable to pay the amount agreed in the contract only when the specified event has occurred. Hence, they are basically one-sided contract where only offeror has to fulfill the promises of the agreement but only when the act mentioned in the contract has taken place.

Example of such contract is health insurance policy in which companies pays the designated amount to insurer in cases if he faces any health-related issue. The conditions of health are pre-defined in the contract.

Based on the definition option D is correct option.

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