题目

If women are mercilessly exploited（剥削）year after year， they have only themselves to blame. Because they tremble at the thought of being seen in public in clothes that are out of fashion， they are always taken advantage of by the designers and the big stores. Clothes which have been worn only a few times have to be put aside because of the change of fashion. When you come to think of it， only a woman is capable of standing in front of a wardrobe（衣柜）packed full of clothes and announcing sadly that she has nothing to wear. Changing fashions are nothing more than the 已知x=2y=1是方程组ax-by=1x+by=5的解，则a、b的值分别为（　　） A、2，7B、-1，3C、2，3D、-1，7