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（）.
单项选择题 Corrosive liquids and acids should have which kind of label?（）
单项选择题 Conventional anchors are least likely to hold in a bottom consisting of（）.
