在数控加工中，加工凸台、凹槽时选用____刀。
参考答案：立式端铣
简述不落家形成的原因.
— Would you like to climb mountains with me this afternoon?
— I'd love to. But I ____ play table tennis between classes. [ ]
A. am going
B. am going to
C. am
D. going to
