Which of the Following Is True About the Exception to the Parol

Which of the following is true about the exception to the parol evidence rule?

A) A party can always introduce proof of an oral agreement made after the writing was created,these subsequent oral modifications of contracts will always be enforceable.
B) A party can introduce oral testimony about the facts and circumstances surrounding the agreement without contradicting its terms.
C) A party can always introduce proof of an oral agreement made before the writing was created,these oral agreements will always be enforceable.
D) If the terms of the writing are unclear,oral testimony can be introduced to aid the court in interpreting the writing.