（）indicates unstable weather.

单项选择题（）may be a warning for an approaching storm.

A.The persence of cirrus clouds
B.The low-hanging stratus clouds
C.The altocumulus clouds
D.The massive cumulus clouds

单项选择题Nimbus means（）.

A.rain
B.high
C.layer
D.cirrus

单项选择题Alto stands for（）.

A.rain
B.high
C.layer
D.cirrus

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

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