A.low barometric pressureB.high barometric pressureC.fa……

单项选择题Fog forms when the air（）.

A.Is 50% water saturated
B.Is 90% water saturated
C.Temperature is greater than the dew point temperature
D.Temperature is equal to，or below the dew point temperature

单项选择题Fetch is the（）.

A.Distance a wave travels between formation and decay
B.Stretch of water over which a wave-forming wind blows
C.Time in seconds required for two crests to pass a given point
D.Measurement of a wave's steepness

单项选择题Cyclones that have warm sectors usually move（）.

A.westerly
B.parallel to the isobars in the warm sector
C.toward the nearest high pressure area
D.faster than the accompanying cold front

单项选择题Cumulus clouds that have undergone vertical development and have become cumulonimbus in form，indicate（）.

A.clearing weather
B.that a warm front has passed
C.probable thunderstorm activity
D.an approaching hurricane or typhoon

单项选择题Cumulonimbus clouds are formed by（）.

A.vertical air movements
B.heavy rainstorms
C.horizontal air movements
D.any movement of moist air