单项选择题
A.2 B.3 C.4 D.5
A.2块,2mm B.3块,3mm C.2块,3mm D.3块,2mm
A.φ4mm,φ3mm B.φ3mm,φ4mm C.φ5mm,φ4mm D.φ4mm,φ5mm
A.1块 B.2块 C.3块 D.4块
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