A.Low cl;oudsB.High cloudsC.Special cloudsD.medium clou……

单项选择题（）is a high layer of cloud in the front of small flakes or cauhflower,white in colour with no dark shadows in between.

A.Cirrostratus
B.Cirrus
C.Cirrocumulus
D.Altostratus

单项选择题（）is a silvery cloud in the front of feathers or fibres seen high up against a blue sky.

A.Cirrostratus
B.Cirrus
C.Cirrocmulus
D.Altostratus

单项选择题（）are mainly caused by the gravitational pull of the moon.

A.Tides
B.Sea
C.Swell
D.Wind

单项选择题（）generally indicates that a gale or storm is approaching.

A.Falling barometric pressure
B.Rising barometric pressure
C.The circulations of winds
D.The change of wind direction

单项选择题（）indicates unstable weather.

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