In Which of the Following Circumstances Is a Debt Settlement

In which of the following circumstances is a debt settlement a binding contract?

A) Where the amount of the debt is uncertain or subject to dispute.
B) Where the amount of the debt is certain and undisputed.
C) Where the only consideration the creditor gives the debtor is his promise not to sue the debtor on the original debt.
D) Where the settlement is part of a composition agreement.