In Which of the Following Situations Is Consideration Required

In which of the following situations is consideration required?

A) An agreement modifies a sales contract.
B) A promise to act a pre-existing duty.
C) The contract does not bind the promisor to give up anything.
D) A person promises a benefit to someone to do something which the promisee is already disallowed from doing.
E) A voidable promise has been renewed by the promise.