题目

He achieved great success but only at the _______ of a happy family life. A. cost                       B. risk               C. time                   D. sight 答案：A若命题p的逆命题是q，命题p的否命题是r，则q是r的(    )A.逆命题                  B.否命题            C.逆否命题          D.以上都不对