防止螺栓、螺母咬口的措施是要求用于螺母材料的硬度比螺杆材料的硬度要低()。
A.15~20HB;
B.20~40HB;
C.40~60HB;
D.10~15HB。
参考答案:B
The heart is believed to _____blood into veins(血管) which are netted all over the body, thus keeping a person alive. [ ]
A. give
B. donate
C. circulate
D. pump
保证零部件互换性,允许加工的误差称为()
A.配合
B.公差
C.形位公差
D.偏差