单项选择题

After putting on a self-contained breathing apparatus，you open the air supply and hear a continuous ringing of a bell. What does this mean? （）

A.The unit is working properly
B.The face mask is not sealed properly
C.The air bottle needs to be refilled
D.The air supply hose has a leak

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热门试题

单项选择题According to the Chemical Data Guide，epichlorohydrin is a(n)（）.

A.corrosive
B.class B poison
C.oxidizer
D.explosive

单项选择题A space should be ventilated when（）.

A.The cargo's temperature is colder than the dew point of the air in the space
B.The cargo's temperature is warmer than the dew point of the air in the space
C.The dew point of the air in the space is lower than the dew point of the outside air
D.All of the above

单项选择题（）is the most liable to spontaneous combustion.

A.Cement
B.Chinaware
C.Fish meal
D.Steel products