单项选择题
A.6mm B.10mm C.15mm D.20mm
A.50% B.70% C.80% D.95%
A.1.2N/mm2B.2.4N/mm2C.3.6N/mm2D.4.8N/mm2
A.2;3 B.3;2 C.1;2 D.5;4
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