单项选择题
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
Foam-type portable fire extinguishers are most useful i...
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
Foam is a very effective smothering agent and（）.A.it pr...
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
Foam extinguishes a fire mainly by（）.A.coolingB.chemica...
单项选择题Foam extinguishes a fire mainly by（）.
A.cooling B.chemical action C.smothering D.inerting the air
