现代教育在17世纪夸美纽斯的教育思想中就已经有了比较充分的表露;但作为一种制度则是在19世纪初以后系统确立起来的,以()的确立为标志。
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()of the following conditions will cause a vessel’s bottom to be subjected to tension stresses.
A. Concentration of weight aft
B. Concentration of weight forward
Concentration of weight amidships
D. Concentration of weight at both ends of the vessel