题目内容

关于静力学中约束的概念，以下表述错误的是

A. 约束反力、约束力和反力是同一个概念；
B. 习惯上把构成约束条件的周围物体称为约束；
C. 约束力的大小和方向只与作用于非自由体的主动力有关；
D. 主动力是指那些能够使物体产生运动或运动趋势的力。

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三力平衡定理是

A. 刚体受不共面三个力作用时也可能平衡。
B. 三力汇交于一点，则这三个力必互相平衡
C. 共面不平行的三个力互相平衡必汇交于一点。
D. 共面三力若平衡，必汇交于一点

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A. 膨松剂
B. 乳化剂
C. 抗结剂
D. 抗氧化剂

硅酸钙在吸收较多水分或其他液体后都是流动性粉末，但可与___形成凝胶。

A. 无机酸
B. 有机酸
C. 弱碱液
D. 强碱液