单项选择题

In many areas atoll clouds (clouds of vertical development) are produced over small islands. These are the result of（）.

A.rising air currents produced by the warm islands
B.warm air from the sea rising over higher land areas
C.cool land air mixing with warm sea air
D.descending air over the islands

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单项选择题In a microbarograph，the pen should be checked and the ink well filled（）.

A.each time the chart is changed
B.once per month
C.once per week
D.daily

单项选择题If an observer in the Northern Hemisphere faces the surface wind，the center of low pressure is to his（）.

A.left，slightly behind him
B.right，slightly behind him
C.left，slightly in front of him
D.right，slightly in front of him

单项选择题Cyclones tend to move（）.

A.perpendicular to the isobars in their warm sectors
B.parallel to the isobars in their warm sectors
C.parallel to the line of the cold front
D.perpendicular to the line of the cold front

单项选择题Cumulonimbus clouds can produce（）.

A.dense fog and high humidity
B.gusty winds，thunder，rain or hail，and lightning
C.clear skies with the approach of a cold front
D.a rapid drop in barometric pressure followed by darkness

单项选择题Cumulonimbus clouds are most likely to accompany a(n)（）.

A.high pressure system
B.cold front
C.warm front
D.occluded front