Would a Letter Written After the Execution of a Contract

Multiple Choice

Would a letter written after the execution of a contract and which contained agreements different from those in the written contract be admissible under the parol evidence rule?

A) No, because it contradicts the terms of the contract.
B) No, because it changes the agreement.
C) No, because it explains the agreement.
D) Yes, it would be admissible, because it is subsequent to the written agreement.