Cyril Owed Robert $12,000 but Since He Had Lost His

Cyril owed Robert $12,000 but since he had lost his job,he could pay only $7,000.Reluctantly,Robert agreed,since they were old friends,to accept the lesser amount as full payment of the debt,and Cyril gave him the money.Now Robert has heard that Cyril has just won a huge amount in a lottery but Cyril will not pay him the rest of the debt."A deal's a deal," Cyril says.

A) Since Cyril gave no consideration for Robert's promise to forgive the rest of the debt,Robert can successfully sue him for the balance.
B) While Robert would have been able to sue Cyril under Common Law,statute law says that,having accepted part of the debt as payment for the full amount,Robert cannot now demand the balance.
C) Whether or not Robert could successfully sue for the balance of the debt,the courts would not allow a debtor to be unjustly enriched in this way and would order Cyril to pay Robert the balance of the debt.
D) a and c.
E) b and c.