Brief，violent showers frequently accompanied by thunder and lightning are usually associated with（）.

单项选择题As a cold front passes an observer，pressure（）.

A.drops and winds become variable
B.rises and winds become gusty
C.drops and winds become gusty
D.rises and winds become variable

单项选择题An occluded front is usually caused by a（）.

A.cold front becoming stationary
B.warm front becoming stationary
C.cold front overtaking a warm front
D.warm front dissipating

单项选择题An occluded front is caused by a(n)（）.

A.low pressure area
B.high pressure area
C.area of calm air
D.cold front overtaking a warm front

单项选择题An instrument designed to maintain a continuous record of atmospheric pressure is a(n)（）.

A.mercurial barometer
B.aneroid barometer
C.barograph
D.thermograph

单项选择题An atoll cloud forming over an island due to heating of the land during the daytime would be which type? （）

A.Cirrus
B.Cumulus
C.Stratus
D.Nimbus