单项选择题
A.the man has been missing for a period of time
B.the sea water is very cold and the man is visible
C.there is thick fog
D.the wind was from astern on the original course
单项选择题 While moving ahead，a twin-screw ship has an advantage over a single-screw ship because （）.
单项选择题 When towing astern，one way to reduce yawing of the tow is to（）.
单项选择题 When a vessel navigates in an area with a small underkeel clearance but with adequate space to take avoiding action she（）.