And then I ask you do you think this's the same train as the train we pointed to before.

之后我问你,你认为这辆火车,和之前看到的是同一辆吗。

耶鲁公开课 - 死亡课程节选

The first one will be above and below the bond axis is where we'll see the electron density, and the second will be perpendicular to that, so it will be a density in front of and behind the bond axis.

第一个是在键轴之上和之下,我们可以看到电子密度，另外一个垂直于它，所以在键轴之前和之后有电子密度。

麻省理工公开课 - 化学原理课程节选