A.60m B.40m C.25m D.20m
A.50mm B.60mm C.75mm D.90mm
A.2对 B.4对 C.6对 D.8对
A.3mm B.6mm C.9mm D.12mm
A.70m B.60m C.40m D.30m
A.拉应力 B.压应力 C.剪应力 D.拉应力与压应力
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