单项选择题
A.serves as a sea painter
B.detaches automatically
C.is used to rig the boarding ladder
D.is cut immediately as it is of no further use
单项选择题 Advection fog may be formed by cold air passing over a（）.
单项选择题 A sea anchor is（）.
单项选择题 A mercurial barometer at sea is subject to rapid variations in height (“pumping”) due to the pitch and roll of the vessel. To avoid this error，measurements of atmospheric pressure at sea are usually measured with a(n)（）.