System is the research object of the control theory.

控制理论研究的对象是系统。

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The economic growth problem is the most important research object of economics theory.

经济增长问题是经济学理论研究中最重要的对象。

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The economic growth problem is the most important research object of economics theory.

经济增长问题是经济学理论研究中最重要的对象。

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