Janice offers Greg $20 to take some items to the town dump for her. Greg responds, "Sure, if I'm not using my truck to help my friend move I can probably do it." This exchange likely would be considered: O A. an unenforceable contract on the basis of inadequate consideration (illusory promise) B. a valid, enforceable contract O C. an entorceable requirements contract D. enforceable due to promissory estoppel