Which of the Following Is Not a Circumstance Where a Court

Which of the following is not a circumstance where a court will admit verbal evidence when determining the terms of a contract?

A) To establish that a written contract is invalid or unenforceable for some reason.
B) To establish that one party is acting as an agent for someone else.
C) To incorporate common trade usage not referred to in the written contract.
D) To vary the terms of a written contract even where that contract appears to be a complete record of agreement.