单项选择题
From which type of cloud can a tornado or waterspout develop?（）
A.Nimbostratus B.Altostratus C.Cumulonimbus D.Cirrus
单项选择题 Freeboard is measured from the upper edge of the（）.
单项选择题 Frapping lines（）.
单项选择题 Forty-five fathoms is marked on the anchor chain by（）.
