题目

 — I was told to be here at this time. —Sorry, you              . I forgot to tell you we've changed the plan.   A. mustn't                                   B. can't                             C. needn't              答案：C方程2x2-=0的解是A.x1=x2=2B.x1=x2=C.x1=2，x2=-2D.x1=，x2=-