What Is Required for a Claim in Promissory Estoppel to Succeed

What is required for a claim in promissory estoppel to succeed?

A) Promissory estoppel is not a cause of action. Rather, it is a mechanism to stop the representee relying on his rights in contradiction to the representation he made.
B) It is inequitable or unconscionable to go back on a clear and unequivocal promise.
C) Reliance by the promisee on that promise.
D) Both option b) and (c) .