A.warm frontB.tropical cycloneC.anticycloneD.cold front……

单项选择题In the Northern Hemisphere，an area of counterclockwise wind circulation surrounded by higher pressure is a（）.

A.low
B.high
C.warm front
D.cold front

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

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