A long-time client of a law firm calls and is upset. The client's mentally handicapped brother has just been tricked into buying an expensive laptop computer

The client, who is the guardian for his brother, wants to make the merchant void the sale and refund the money. The best argument for this might be:
A) the brother lacks capacity to enter into a contract.
B) the contract should be in writing.
C) the Parol Evidence Rule was violated.
D) the Statute of Frauds was violated.

A