单项选择题
A.60° B.80° C.90° D.180°
A.调心轴承B.滚动轴承C.向心轴承D.推力轴承
A.轴 B.蜗杆 C.蜗轮 D.键
A.10%~45% B.40%~50% C.50%~60% D.60%~70%
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