题目

 A hard-working man _____ become a great scientist, but a great scientist _____ be a hard-working man.    A. can’t, can          B. may not, can      C.can’t, must     D. may not, must 答案：D已知圆，从点发出的光线，经轴反射后恰好经过圆心，则入射光线的斜率为（ ）A． B． C. D．