Which Doctrine May Courts Use to Estop,or Prevent,an Offeror from Revoking

Multiple Choice

Which doctrine may courts use to estop,or prevent,an offeror from revoking an offer based on a party's taking steps in reasonable reliance on an offer?

A) Promissory estoppel
B) Consideration reliance
C) Contract enforcement
D) Ethical reasoning
E) True to form