单项选择题
A.1% B.2% C.10% D.20%
A.1mm B.2mm C.3mm D.4mm
A.低碳钢 B.中碳钢 C.高碳钢 D.低合金钢
A.小于2.11% B.大于2.11% C.小于0.25% D.大于0.25%
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