题目

 He has been used to            . A. practice playing piano every day                      B. practice to play the piano every day C. practicing playing the piano every day            D. practicing playing piano every day 答案：C 一元二次方程x2﹣2x﹣4=0和x2﹣x+2=0所有实数根的乘积等于(     ) A．﹣8   B．﹣4   C．8       D．4