前面已经简单地介绍了单例模式的实现方式，现在让我们进入主题：两个单例对象如何同时存在？

Now that we've looked briefly at implementation, let's turn to the heart of this article: how two singletons can exist simultaneously.

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Now let's get onto the course topic for today, which is food and evolution.

现在我们要进入今天的主题,即食品和人类演化

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选