单项选择题
A.Low cl;ouds B.High clouds C.Special clouds D.medium clouds
（）is a high layer of cloud in the front of small flakes...
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
（）is a silvery cloud in the front of feathers or fibres...
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
（）are mainly caused by the gravitational pull of the mo...
单项选择题（）are mainly caused by the gravitational pull of the moon.
A.Tides B.Sea C.Swell D.Wind
