To define a subject, you create a DITA topic (typically a concept topic) to identify an aspect of the subject matter of your content (see Figure 2).

要定义主题，需要创建DITA题目(通常是内容题目)来标识内容的主题问题方面(请参阅图2)。

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The topic, subject, or concept you want to learn doesn't matter.

你想学习的话题、主题或概念并不重要。

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Preface by painting a clear concept of dark subject matter, as well as literature and academic status of order, the establishment of research ideas and topics of this paper significance.

前言部分通过明确黑暗题材绘画的概念，以及对文献资料和学术状况的整理，确立本文的研究思路和选题意义。

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