Which of the Following Is Not Required for Promissory Estoppel

Which of the following is not required for promissory estoppel to apply?

A) The promise made must be reasonable.
B) The promise made must be relied on by the promisee to the promisee's detriment.
C) The promisor must suffer an injustice if the promise isn't enforced.
D) The promisor must know that the promisee is likely to rely on the promise.