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 （）.

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

单项选择题A vessel travelling down a narrow channel，especially if the draft is nearly equal to the depth of the water，may set off the nearer side. This effect is known as（）.

A.smelling the bottom
B.squatting
C.bank suction
D.bank cushion

单项选择题A vessel towing astern in an operation which severely restricts the towing vessel and her tow in their ability to change course shall，when making way，exhibit（）.

A.the masthead lights for a towing vessel
B.the lights for a vessel restricted in its ability to maneuver
C.sidelights，sternlight and towing light
D.All of the above

单项选择题A vessel is equipped with a single right-handed screw. With rudder amidships and calm wind，the vessel will most likely back（）.

A.straight astern
B.to port
C.to starboard
D.in no particular direction