单项选择题
A.each time the chart is changed B.once per month C.once per week D.daily
If an observer in the Northern Hemisphere faces the sur...
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
Cyclones tend to move（）.A.perpendicular to the isobars ...
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
Cumulonimbus clouds can produce（）.A.dense fog and high ...
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
