单项选择题
A.controls the amount of gasoline to the engine
B.shuts off the gasoline supply at the tank
C.is used if the gasoline tank leaks
D.All of the above
单项选择题 The primary hazard of liquefied petroleum gas and liquefied natural gas is（）.
单项选择题 The amount of LFG that may be loaded into a given tank is determined by（）.
单项选择题 The airborne concentrations of substances (such as H2S) under which nearly all workers may be repeatedly exposed without adverse effects are called（）.