基准代号由基准符号、圆圈、（）组成。
A.三角形
B.数字
C.弧线
D.连线和字母
参考答案：D
He's given an important report on the work of the government, ________? [ ]
A. isn't he
B. is he
C. hasn't he
D. has he
二分器格槽的开口尺寸最少不应小于（）mm。
A、3
B、4
C、5
D、6
