单项选择题
A.the relative humidity is 100%
B.the vapor pressure is at its minimum for the prevailing temperature
C.precipitation has commenced
D.cloud cover is 100%
单项选择题 The broadcast will normally be made on the two listed frequencies simultaneously except during transmitter maintenance periods when the broadcast will be made on the two frequencies（）.
单项选择题 THE ANCHOR WAS HEAVED AWEIGH means（）.
单项选择题 The abbreviation RYC in a marine cable generally stands for（）.