Cyclones that have warm sectors usually move（）.

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

单项选择题Corrosive liquids and acids should have which kind of label?（）

A.Skull and crossbones
B.Yellow and white
C.Red and white
D.White and black

单项选择题Conventional anchors are least likely to hold in a bottom consisting of（）.

A.soft clay
B.hard mud
C.very soft mud
D.sand

单项选择题Control of fire should be addressed（）.

A.immediately after restoring vital services
B.immediately
C.following control of flooding
D.following establishment of fire boundaries