电动伸缩门（豪华不锈钢型的）不锈钢的厚度的尺寸一般为多少?有5.5的吗,如0.8那单位是什么?

解题思路：三角形具有稳定性，不容易变形．平行四边形与三角形不同，容易变形，也就是具有不稳定性．这种不稳定性在实践中有广泛的应用，电动伸缩门是利用平行四边形具有不稳定性的特点制成的，进行解答即可．

由分析可知：电动伸缩门通常是运用了平行四边形易变形的特性；
故选：B．

点评：
本题考点： 平行四边形的特征及性质．

考点点评： 本题是考查平行四边形的特征及性质．

解题思路：由平行四边形的特性可知，平行四边形具有不稳定性，所以容易变形，伸缩门运用了平行四边形易变形的特性．

伸缩门做成平行四边形的形状，是利用平行四边形的易变形的特性．
故选：B．

点评：
本题考点： 平行四边形的特征及性质

考点点评： 此题主要考查了平行四边形的特性是容易变形．

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