$38.$ Mike innocently says that his guitar was twenty years old. In fact, the guitar was thirty$-$five years old. John, who bought the guitar from Mike, admits that he would have bought the guitar so long as it was not more than fifty years old. However, John still wants to rescind the deal. Under these circumstances:

a$.$ John can rescind the contract under the theory of fraudulent misrepresentation.

b$.$ John cannot rescind the contract because the misrepresentation was not material.

c$.$ John can rescind the contract because of unilateral mistake of fact.

d$.$ John can rescind the contract under the theory of mutual mistake.