单项选择题
A.45°B.60°C.75°D.90°
A.0.1~0.5B.0.2~0.6C.0.2~0.5D.0.1~0.6
A.1/6B.1/8C.1/9D.1/10
A.1:2B.1:3C.1:4D.1:5
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