单项选择题
A.the direction of the true wind
B.true north
C.the beam on the windward side
D.the beam on the lee side
单项选择题 In modern fathometers the sonic or ultrasonic sound waves are produced electrically by means of a(n)（）.
单项选择题 In mid-ocean，the characteristics of a wave are determined by three factors. What is NOT one of these factors?（）.
单项选择题 In a tropical cyclone，in the Northern Hemisphere，a vessel hove to with the wind shifting counterclockwise is（）.