So what I want to point out about them is that they're made up of two nodes, and what you can see is that nodes are shown in different colors here and those are different phases.

关于它们我要指出的是,它们有两个节点，你们可以看到在这里,这些节点的颜色不同，它们的相位不一样。

麻省理工公开课 - 化学原理课程节选