Which of the Following Is True of the Parol Evidence

Which of the following is true of the parol evidence?

A) It discourages parties from signing a no-competition clause.
B) It prevents a party from varying the terms of a written contract by claiming the existence of contradictory oral terms.
C) It provides a set of exceptions to the statute of frauds.
D) It prevents the unjust enrichment of a party who has refused to perform pursuant to clear contract terms.