Answer:
b. only one promise is involved in a unilateral contract.
Step-by-step explanation:
An unilateral contract is a contract where the person or the offeror making the contract promises for the execution of the task by the other party. It can be accepted only be a performance.
In unilateral contract, there is only one promisor and no promisee is required whereas is bilateral contract includes both the promisor and the promisee.
Thus the correct answer is
b. only one promise is involved in a unilateral contract.