它是由递归下行复合数据结构引起的，这种下行方式有时在一次递归调用中要下行多级。

It is caused by recursively descending a composite data structure in such a way that, sometimes, more than one step in the descent is taken in a single recursive call.

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有时，一次用多级齿轮传动可获得大的降速比。

Sometimes, many spur gears are used at once to create very large gear reductions.

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据此，作者认为黄土可以不是一次完成浸水湿陷，具多级湿陷特性。

Here by, the authors conclude that loess collapsibility has character of multilevel.

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