单项选择题
The proximity of pack ice may be indicated by（）.
A.changes in seawater salinity B.glare on clouds on the horizon C.changes in air temperature D.icebergs
单项选择题 Small floes of rough，hummocky sea ice capable of damaging a vessel（）.
单项选择题 On a twin-screw，twin-rudder vessel，the most effective way to turn in your own water，with no way on，is to put（）.
单项选择题 On a single-screw vessel the stern frame（）.
