A gas-free certificate would usually be issued by a(n)().
ABS marine surveyor
B. certified marine chemist
C. port engineer
D. Coast Guard marine inspector
C620-1车床上加工螺纹,丝杆螺距为12mm,车削螺距为()mm螺纹不会产生乱扣。
A. 1.25
B. 1.75
C. 2
D. 2.5
从六氟化硫气瓶引出气体时,应使用减压阀降压。当瓶内压力降至()MPa时,即停止引出气体,并关紧气瓶阀门,戴上瓶帽。
A. 0.1
B. 0.2
C. 0.3
D. 0.4