I don't know how well you can see it in this figure here, is the slope of a straight line connecting these two points, and as the points come closer and closer, the straight line would become tangent to the curve.

我不清楚你们对于这个图像的理解,这条连接两点的斜线,随着两点距离逐渐缩小,两点连线会变成曲线的切线

耶鲁公开课 - 基础物理课程节选

Now if you read in the book, you read about where this figure is shown in the book, you can understand more about why these structures line up in the right way so that the right molecular elements are together to form hydrogen bonding pairs between them.

如果你预习过课本,课本中有关于这些详细的描述,你可以更深刻的理解,为什么这些结构是采用这种连接方式,以使对应的分子部分靠近,并形成氢键连接

耶鲁公开课 - 生物医学工程探索课程节选