单项选择题
A.直立式B.斜倾式C.横卧式D.下垂式
A.1/6-1/5B.1/5-1/3C.1/3-1/2D.1/2-2/3
A.3B.4C.5D.6
A.1/5-/1/4B.1/4-1/3C.1/3-1/2D.1/2-2/3
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