There Is an Existing Contract Calling for Seller to Deliver

There is an existing contract calling for Seller to deliver 1,000 widgets to Buyer.Buyer says to Seller,"I would like to buy 100 additional units at the same price." Seller responds,"We promise to sell you the 100 extra units if we decide not to sell them to other customers." Regarding only the sale of the extra 100 units:

A) There is no consideration due to an illusory promise.
B) There is no consideration due to a preexisting duty.
C) There is no consideration due to a past consideration.
D) There is consideration due to promissory estoppel.
E) There is consideration due to a legal detriment on both sides.