单项选择题

Gas masks（）.

A.should be worn while fighting a fire
B.can be used in atmospheres deficient in oxygen
C.filter contaminants from air that is to be breathed
D.may be substituted for a self-contained breathing apparatus

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单项选择题

Fusible-link fire dampers are operated by（）.

A.8the heat of a fire melting the link
B.a break-glass and pull-cable system
C.electrical controls on the bridge
D.a mechanical arm outside the vent duct

单项选择题

Foam-type portable fire extinguishers are most useful in combating fires involving（）.

A.solid materials such as wood or bales of fiber
B.inflammable liquids
C.electrical equipment
D.metallic solids

单项选择题

Foam is a very effective smothering agent and（）.

A.it provides cooling as a secondary effect
B.works well on extinguishing electrical fires
C.can be used to combat combustible metal fires
D.All of the above