this time the design of airships was constantly being improved and1937 they carried thousands of passengers on regulartransatlantic services for millions of miles.
A. During / then
B. Until / then
C. During / up to
D. While / until
E. Whenever / until
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the surrounding rocks contain copper, the stalactites are green.
A. Whereas
B. Along
C. Whenever
D. Through
E. While
现有两种说法： ①弹性变形中，σ-ε一定是线性关系②弹塑性变形中，σ-ε一定是非线性关系 ；哪种说法正确？
A. ①对②错
B. ①对②对
C. ①错②对；
D. ①错②错；
两杆几何尺寸相同，轴向拉力F相同，材料不同，它们的应力和变形可能是 。
A. 应力σ和变形△ι都相同
B. 应力σ不同，而变形△ι都相同
C. 应力σ相同，变形△ι不同
D. 应力σ和变形△ι都不同
一拉压杆的抗拉截面刚度EA为常量，若使总伸长为零，则必为零。
A. 杆轴力图面积的代数和
B. 杆内各点处的位移
C. 杆内各点处的正应力
D. 杆内各点处的应变
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