单项选择题
Dacron sails，when not in use，may be damaged if（）.
A.left in the sunlight B.stowed wet C.washed with soap D.folded frequently
单项选择题 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（）.
单项选择题 Cumulonimbus clouds are formed by（）.
