单项选择题
A.116°~118° B.120°~125° C.135°~150° D.90°~100°
A.116°~118° B.130°~140° C.90°~100° D.125°~130°
A.上方 B.下方 C.右侧 D.左侧
A.低碳钢 B.中碳钢 C.高碳钢 D.铸铁
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