题目

质量为M的物块以速度v运动，与质量为m的静止物块发生正碰，碰撞后两者的动量正好相等，则两者质量之比为M/m可能为                         （    ）        A．2                        B．3                        C．4                        D．5 答案：ABJudging from the date _______ on the gold coin, we can tell that it was made 500 years ago.   [     ]A. being marked  B. marked        C. to mark          D. to be marked