What Is the Difference Between an Agreement and a Contract

What is the difference between an agreement and a contract?

A) An agreement results whenever two people's minds meet on a subject, but a contract only exists when the parties intend to be legally obligated by the terms of the agreement.
B) An agreement must be put in writing, whereas a contract may be made orally.
C) An agreement is binding for a shorter period of time than a formal contract.
D) An agreement may be made for an unlawful purpose, whereas a contract must be made for a lawful purpose.