对概念主题的引用，个数不限。

References to any number of concept topics.

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清单1展示的例子是一个针对轴承的概念主题。

Listing 1 shows an example of a concept topic for mechanical bearings.

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概念主题通过定义术语和解释概念提供了任务背后的原因。

Concept topics provide the reason behind the tasks by defining terms and explaining concepts.

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Let's move on to the last topic in terms of this first exam, which is thinking about the idea of isoelectronic atoms, or isoelectronic ions. And isoelectronic is very straightforward, it just means having the same electron configuration.

下面我们继续讲第一次考试的最后一个主题，也就是等电子原子，或等电子离子的概念，“等电子的“是非常直接的表达，它的意思就是具有相同电子排布的。

麻省理工公开课 - 化学原理课程节选