Which of the Following Shows the Use of the Doctrine

Which of the following shows the use of the doctrine of promissory (equitable) estoppel?

A) A defendant can use this doctrine as a defence against a plaintiff insisting on his full legal right when he had promised to forgive the defendant some of his obligation.
B) Ralph told Mary that he would give her his old boat. If he doesn't, Mary could use the doctrine to force him to do so.
C) If Ho requests services from Jones and there is no mention of price, if Ho doesn't pay Jones, this doctrine can be used to force Ho to pay a reasonable amount.
D) If Nancy accidentally ran her car over her neighbour's bushes, she could use the doctrine as a defence.
E) This doctrine can be used by a plaintiff to enforce a written promise signed and sealed (i.e., a seal has been affixed next to the signature of the promisor) .