Final answer:
A contract is a legally enforceable agreement under which two parties agree to do something for each other.
Step-by-step explanation:
The correct answer is A) Contract. A legally enforceable agreement under which two parties agree to do something for each other is called a contract. Contracts can be written or oral, and they involve obligations and rights for each party involved. For example, when you sign a contract to purchase a product or hire a service, you are entering into a legally binding agreement with the other party. The terms of the contract define what each party should do and what they are entitled to.