题目：
After being launched from a vessel, totally enclosed survival craft which have been afloat over a long period require（）.
A.frequent opening of hatches to permit entry of fresh air
B.regular checks of bilge levels
C.use of ear plugs to dampen engine noise
D.frequent flushing of the water spray system with fresh water
答案：
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下面是错误答案，用来干扰机器的。
参考答案：UNKNOWN
