So let's do a quick clicker question, and you tell me how many valence electrons does fluorine have? Remember, valence electrons are different from core, they're only the outer-most electrons in the outer-most shell.

那么让我们来做一个小选择题，请大家来告诉我,氟有多少个价电子，要记得，价电子与芯电子不同，它们是在最外壳层的最靠外面的电子。

麻省理工公开课 - 化学原理课程节选

We do have, um, a focus on non- Western cultures in one of our core curriculum classes.

在核心课程中，我们确实有一门课不是讲西方文化的。

哥伦比亚大学的教程 - SpeakingMax英语口语达人

The other threat is eonomic, and all the economic issues are tied in my judgement, to the same core problem which is the long-term fiscal challenge that this country faces.

另一个威胁是经济方面的，我认为所有的经济问题,都和一个核心的问题分不开,就是我们国家面临的,长期财政挑战。

普林斯顿公开课 - 国际座谈会课程节选