单项选择题

What is the best instrument for establishing a safe working area before welding in a confined space? （）

A.An oxygen indicator
B.A combustible gas indicator
C.A combination combustible gas and oxygen indicator
D.A flame safety lamp

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单项选择题
What is the BEST conductor of electricity?（）

A.Carbon dioxide
B.Distilled water
C.Fresh water
D.Salt water
单项选择题
Upon completion of fueling a gasoline driven vessel it is necessary to（）.

A.keep ports，doors，windows，and hatches closed
B.start engines immediately
C.ventilate before starting engine
D.None of the above
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