单项选择题
A.gradient current B.density current C.swift current D.torrent current
（）is the most widespread type likely to be encountered ...
单项选择题（）is the most widespread type likely to be encountered at sea and is caused by relatively warm air being cooled by flowing over a cooler sea surface.
A.FRONTAL FOG B.MIXING FOG C.ADVECTION FOG D.RADIATION FOG
（）is a type of fog occurring close to the sea surface w...
单项选择题（）is a type of fog occurring close to the sea surface when the air is dry and cold-probably at least 9℃ below the sea surface temperature.
A.MIXING FOG B.ADVECTION FOG C.RADIATION FOG D.ARCTIC SEA SMOKE
（）forms over land，most frequently during autumn and win...
单项选择题（）forms over land，most frequently during autumn and winter over low-lying land，especially if it is damp and marshy and in valleys on quiet nights with clear skies.
