单项选择题
An example of a messenger is a（）.
A.fairlead B.heaving line C.stay D.warp
单项选择题 All electrical appliances aboard a vessel should be grounded to（）.
单项选择题 All echo-sounders can measure the（）.
单项选择题 Aboard ship，vertical flat plates running transversely and connecting the vertical keel to the margin plates are called（）.
