An occluded front is usually caused by a（）.

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

单项选择题Advection fog is most commonly caused by（）.

A.air being warmed above the dew point
B.saturation of cold air by rain
C.a rapid cooling of the air near the surface of the Earth at night
D.warm moist air being blown over a colder surface

单项选择题Advection fog holds longest over which portions of the lakes? （）

A.Northwest
B.Southeast
C.Northeast
D.Southwest