单选题Firefighting foam is only effective when the foam（）.Apenetrates to the bottom of the fireBis kept saturated with low-velocity water fogCmixes with the burning fuel oilDcompletely covers the top of the burning liquid
单选题
Firefighting foam is only effective when the foam（）.
A
penetrates to the bottom of the fire
B
is kept saturated with low-velocity water fog
C
mixes with the burning fuel oil
D
completely covers the top of the burning liquid
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