單項(xiàng)選擇題

As an extinguishing agent,foam（）.

A.couducts electricity
B.should be directed at the base of the fire
C.is most effective on burning gases which are flowing
D.extinguishes by cooling oil fires blow ignition temperature

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單項(xiàng)選擇題

As compared to carbon dioxide,dry chemical has which advantage?（）.

A.Cleaner
B.Effective
C.Greater range
D.More cooling effect

單項(xiàng)選擇題

As oil pipe line connections were broken,（）quantity of oil was caused to spill onto the wharf and into the dock water.

A.a not knowing
B.an unknowing
C.an unknown
D.a not known