A.high pressure systemB.cold frontC.warm frontD.occlude……

单项选择题Clouds that form as small white flakes or scaly globular masses covering either small or large portions of the sky are（）.

A.cirrus
B.cirrostratus
C.altostratus
D.cirrocumulus

单项选择题Clouds are classified according to their（）.

A.size
B.moisture content
C.altitude and how they were formed
D.location in a front

单项选择题Clouds appearing in the following order: cirrus，cirrostratus，altostratus，stratus，and nimbostratus usually indicate the approach of a(n)（）.

A.warm front
B.occluded front
C.medium front
D.cold front

单项选择题Cloud formations are minimal when the（）.

A.surface temperature and temperature aloft are equal
B.surface temperature and temperature aloft differ greatly
C.barometric pressure is very low
D.relative humidity is very high

单项选择题Cirrus clouds followed by cirrostratus then altostratus，stratus，and occasionally nimbostratus indicate the approach of a(n)（）.

A.cold front
B.warm front
C.tropical front
D.occluded front