单项选择题
A.20mm B.24mm C.28mm D.32mm
A.25号钢 B.35号钢 C.45号钢 D.55号钢
A.36mm B.12mm C.30mm D.16mm
A.40Mn钢 B.40Cr钢 C.40MnB钢 D.35CrMo钢
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