Answer:
Bob sues Mark to enforce payment of the check
d. Mark can assert the defense of failure of consideration against Bob.
Step-by-step explanation:
Failure of consideration means that there was no consideration since intended contract between Mark and Sally which would have established the consideration upon Sally's performance was frustrated. The contract did not take effect. It is an established point in contract law that there must be consideration for a contract to be valid and enforceable. Since the contract was not finalized and no performance of consideration was carried out by Sally, she had no legal right to collect Mark's check and endorse it to Bob.
Moreover, any potential contract would have been between Bob and Sally and not Mark. So, Mark can plead failure of consideration in the relationship between him and Sally, thus rendering the check's endorsement to a third party, null and void.