他抚平了包装纸，把它们夹在了书页中间。
He flattened the wrappers and put them between the leaves of his book.
为什么要把复杂数据包装在中间类型中呢？
陈认为如果比例超过上限，要想包装紧密就必须使中间的一些球体不接触圆柱壁，更加复杂。
If the ratio is higher than that, the densest possible pack requires that some of the spheres pack in the middle without touching the cylinder's walls, and that is "more complicated," Chan says.
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