The doctrine of promissory estoppel can be defined as . A. a contract in which a buyer agrees to purchase all of its requirements for an item from one seller B. a contract where the seller agrees to sell all of its production to a single buyer C. an agreement whereby the parties agree to accept something different in satisfaction of the original contract D. an equitable doctrine that prevents the withdrawal of a promise by a promisor if it will adversely affect a promisee who has adjusted his or her position in justifiable reliance on the promise E. a contract which contains a clause that requires one or both of the parties to use their best efforts to achieve the objective of the contrac