In Terms of Requirements for Enforcement of a Contract, What

In terms of requirements for enforcement of a contract, what does consideration mean?

A) Both parties must be considered to be legally able to enter into the contract.
B) Money or something of value must be given in return for fulfilling a contract.
C) The purpose of the contract must be considered to be legal.
D) All persons involved must agree to be bound by the terms of the contract.
E) It must be proven that all parties have considered all possible options before entering into the contract.