Looking back on the bargains Brother Miller had with them, the three young men knew very well that he changed his mind about marbles all the time so that （ ）.
A.正确答案Cthey could learn how to be successful in business
B.they could keep on with their hobby of collection
C.he could offer them something free without hurting their self-esteem
D.he could keep the boys coming to visit his stand and to buy something
