单项选择题
A.12 to 15 times per minute
B.18 to 20 times per minute
C.20 to 25 times per minute
D.as fast as possible
单项选择题 When administering artificial respiration, it is of the utmost important to （）
单项选择题 Safety is dependent on orderliness and cleanlinessOrder may be maintained by （）
单项选择题 To safeguard the operator and other personnel working on or near a hoisting operation which of the following precautions should be observed?（）