单项选择题
A.Rising clouds B.Lowering clouds C.Thickening clouds D.Scattering clouds
（）is formed when the droplets or ice crystals in clouds...
单项选择题（）is formed when the droplets or ice crystals in clouds have become sufficiently large to fall to the ground.
A.Humidity B.Temperature C.Precipitation D.Wind
（）reters to be amount of water vapour in the air.A.Humi...
单项选择题（）reters to be amount of water vapour in the air.
（）is used for receiving maritime safety information whi...
单项选择题（）is used for receiving maritime safety information which is automatically printed by the receiver.
A.NAVETEX receiver B.Search and Rescue Transponder C.Emergency Position Indicating Radio Beacon D.Digital selective calling
