单项选择题
A.45° B.90° C.60° D.都可以
A.90°;90° B.45°;90° C.45°;45° D.60°;90°
A.30°;45° B.45°;45° C.45°;60° D.60°;45°
A.30°;45°B.45°;45°C.45°;60°D.60°;45°
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