Note that some of these lines may already exist, but they could be commented out.
注意，其中一些行可能已经存在，但是可以把它们注释掉。
But they argue that elements of the optimal tax system already exist in some countries.
但他们认为在一些国家存在最优税收理论要素。
But these technologies already exist in some nascent form or another.
但是，这些技术已经初步存在。
Some methods already exist, for example wind power.
有些方法已经存在，例如风力发电。
Some methods already exist, for example wind power.
有些方法已经存在，例如风力发电。
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