小球从空中自由下落，与水平地面相碰后弹到空中某一高度，其速度随时间变化的关系如图所示，g取10m/s²，则

A．0.8s内小球的位移为零

B．0.8s内小球的路程为1.7m

C．0～0.5s与0.5s～0.8s物体的加速度方向相反

D．小球能弹起的最大高度为0.45m

—I think math is _____ English.

—I don't think so. I think English is more difficult. [ ]

A. as useful as

B. as important as

C. as difficult as

D. as interesting as