单项选择题
A.低碳钢 B.中碳钢 C.高碳钢 D.铸钢
A.0.17-0.22 B.0.25-0.6 C.0.6-2.11
A.25°-30° B.30°-35° C.35°-40°
A.15mm B.20mm C.10mm
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