______all  the homework assigned by the school the students have to work at it till midnight

A．Completing

B．To complete

C．Having completed

D．To have completed

为了减少振动，避免锯片铣刀折损，切断时通常应使铣刀外圆（）

A.尽量高于工作底面

B.尽量低于工作底面

C.略高与工作底面