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
单项选择题 What is the BEST conductor of electricity?（）
单项选择题 Upon completion of fueling a gasoline driven vessel it is necessary to（）.
单项选择题 There are（）rats on board.
