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