Answer: d) A unilateral contract
Explanation:
In a unilateral contract there is only one party to the contract that has to abide by the obligations specified and that is the offeror. The offeror offers to pay a certain amount of money if a certain thing is done. They will then pay the person that fulfills this service.
In this case, Darla is the offeror and she offers to pay anyone who can find her cat. When Noelle fulfills this service, Darla will then pay her what was promised. This is therefore a unilateral contract.