单项选择题
A.6 B.7 C.8 D.9
A.圆柱齿轮 B.斜齿轮 C.圆柱、斜齿轮 D.滑轮
A.120.74t B.123.74t C.125.74t D.135.74t
A.220mm B.250mm C.270mm D.290mm
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