单项选择题
A.6 B.5 C.4 D.3
A.φ45.3×3.6 B.φ48.3×3.6 C.φ48.3×3.4 D.φ45.3×3.4
A.12 B.20 C.25 D.30
A.1 B.1.5 C.2 D.3
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