书页通常使用的材料是羊皮纸，羊皮纸是一种动物的皮肤，其在张力的作用下被拉伸和变干，因此它会变得非常平整，并且你可以在上面写字。
The material typically used for the pages was parchment, which is animal skin that's stretched and dried under tension, so it become s really flat and can be written on.
酸性PH值和头发上的微量的负电荷相互作用，以此来帮助毛小皮，即头发表面的一层，保持表面光滑平整。
The acidic pH interacts with the hair's slightly negative charge to help the cuticle, the outer layer of the hair, maintain a smooth, flat surface.
重点介绍了平整轧制对带钢性能的作用及影响。
It focuses on the effect of temper rolling on the strip properties.
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