单项选择题
A.propeller velocity
B.speed of advance
C.wake distribution
D.wake fraction
单项选择题 Apparent wind speed blowing across a vessel under tow can be measured by a(n)（）.
单项选择题 A vessel，which is unable to maneuver due to some exceptional circumstance，shall exhibit （）.
单项选择题 A vessel which through some exceptional circumstance is unable to maneuver as required by these Rules and is therefore unable to keep out of the way of another vessel is called（）.