As demonstrated in Dynegy, Inc. v. Yates, the case in the text, when a contract is determined to be collateral:

A. the principal debtor must pay the guarantor directly.

B. the guarantor must pay, even if the principal debtor is able to do so.

C. it will be unenforceable unless it is evidenced by a writing.

D. proof of an oral agreement is sufficient to prove a contract existed.