对刀点是数控加工中刀具相对（）的起点。
A.机床原点
B.工件
C.尾架
D.换刀点
参考答案：B
——This wall of air is an effective answer to the problem and it ____ work.
——But it is a question to put such a wall of air around the statue.
A．may
B．must
C．should
D．could
铸造用刚玉有（）两种。
