机械坐标系的原点是生产厂家在制造机床时的固定坐标系原点。
参考答案：对
--- What is he doing for vacation?-- He's _______________.[ ]
A. going camp
B. go camp
C. go camping
D. going camping
有助于润肠通便的食物不包括（）
A.浓茶
B.核桃
C.西瓜
D.芝麻
E.香蕉
