At night，a vessel shall indicate that she is restricted in her ability to maneuver by showing in a vertical line two（）.

单项选择题As a vessel falls off the wind from close-hauled to a beam reach，the tendency for the vessel to move sideways through the water will（）.

A.increase
B.decrease
C.change only if the vessel comes about on the opposite tack
D.not change

单项选择题As a ship moves through the water，it drags with it a body of water called the wake. The ratio of the wake speed to the ship’s speed is called（）.

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)（）.

A.barometer
B.wind vane
C.anemometer
D.thermometer

单项选择题A vessel，which is unable to maneuver due to some exceptional circumstance，shall exhibit （）.

A.during the day，three balls in a vertical line
B.during the day，three shapes，the highest and lowest being balls and the middle being a diamond
C.when making way at night，two all-round red lights，sidelights，and a sternlight
D.when making way at night，masthead lights，sidelights，and a sternlight

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（）.

A.a vessel restricted in her ability to maneuver
B.a vessel not under command
C.a vessel engaged in fishing
D.a vessel constrained by her draught