单项选择题
A.rain B.high C.layer D.cirrus
（）is an indication that the weather is about to clear.A...
单项选择题（）is an indication that the weather is about to clear.
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.
