单项选择题
A.1/2 B.2/3 C.3/4 D.1/3
A.10mm B.20mm C.30mm D.7mm
A.HJ431 B.HJ230 C.HJ350 D.HJ250
A.低碳钢 B.低合金钢 C.低碳钢或低合金钢 D.低碳钢和低合金钢
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