Improving the maintainability of a large legacy code base can be very difficult, especially where there is no layering or identifiable structure.

提高大型代码基底的维护性可以是十分困难的，特别是在没有分层或者可识别结构时更是这样。

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Few tree roots or large rocks, which can be very difficult to dig up and extract.

如果遇到一些树根和大石头，非常难搞出来，换地。

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