数控车床X方向对刀时，车削外圆后只能沿（）方向退刀，主轴停转后测量外径尺寸。
A、X
B、Z
C、X、Z都可以
参考答案：B
________I toured Jiu Zhai Gou, I was deeply impressed with his beautiful scenery. [ ]
A. For the first time
B. At first
C. It was the first time
D. The first time
中国标准化协会现有个人会员（）余人，团体会员400余家；下设七个专业标准化分会。
A.40000
B.50000
C.60000
D.30000
