单项选择题
A.VHF communications are basically line of sight
B.the air is more dense the higher you go
C.salt water is a poor conductor of sound
D.sea water absorbs the radiated energy
单项选择题 The generators on your rig have shut down，leaving you without navigation lights. Which emergency signal would you transmit over the VHF radio to alert vessels in the area of your predicament? （）
单项选择题 The expression STAND-BY ENGINE means:（）.
单项选择题 Some goods are missing（）terrible weather.