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（）.
单项选择题 Foam extinguishes a fire mainly by（）.
单项选择题 Foam extinguishes a fire by（）.
