Each hand portable，semi-portable and fixed fire extinguishing unit on a ship must be tested and inspected at least once every（）.<br>A:six weeks<br>B:six months<br>C:twelve months<br>D:two years

Each hand portable，semi-portable and fixed fire extinguishing unit on a ship must be tested and inspected at least once every（）.
A:six weeks
B:six months
C:twelve months
D:two years

出自：海船船员证

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