单项选择题
A cyclone in its final stage of development is called a(n)（）.
A.tornado B.anticyclone C.occluded cyclone or occluded front D.polar cyclone
单项选择题 A cloud sequence of cirrus，cirrostratus，and altostratus clouds followed by rain usually signifies the approach of a(n)（）.
单项选择题 A cloud of marked vertical development (often anvil-shaped) would be classified as（）.
单项选择题 A boundary between two air masses is a(n)（）.
