下面叙述正确的是()。
A. 程序中必须包含有输入语句
B. 变量按所定义的类型存放数据
C. main函数必须位于文件的开头
D. 每行只能写一条语句
Four reciprocal laws are all applicable to ( )
A. The rigid body
B. Linearly elastic system
C. Deformable body
D. Nonlinear system
The method of graph multiplication could be applied to any straight member structure.
Displacement method establishes equations according to on deformation conditions.（ ）
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