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There are two disadvantages to CO₂ pump as a firefighting agent. One of these is the limited quantity available，and the other is（）.
A:the lack of cooling effect on heated materials
B:that it cannot be used in a dead ship situation with no electrical power to the CO₂ pump
C:that it breaks down under extreme heat to form poisonous gases
D:there is no effect on a class A fire even in an enclosed space

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出自：海船船员证

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