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

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