Choice "C" is correct. Under the Statute of Frauds a promise to pay the debt or default of another (a "surety" contract) must be evidenced by a writing signed by the surety (the party to be charged). Decker orally guaranteed the debt owed by Decker's cousin. Thus, Decker's promise is not enforceable. Baker's confirmation is irrelevant.
Choices "d" and "a" are incorrect, because Decker is not liable under the oral guaranty. The guaranty must be evidenced by a writing signed by Decker to be enforceable. Unlike a confirmation between merchants in a sale of goods contract, Baker's confirmation is irrelevant here.
Choice "b" is incorrect. Decker is not liable because Decker did not sign the guaranty. That the promise expired one year after Decker's guaranty is not relevant here.