你可以向上看，向下看，看黑板或者看老师。

You can look up, look down, look at the board or look at the teacher.

youdao

可以让模特向上看，向下看，或者看镜头。

You can have them look up, down or to the camera.

youdao

吊扇可以把空气向上或者向下吹——这取决于吊扇是怎样安装的。

These fans will either blow the air down or up, depending how you set them.

youdao

So what that means is that we're limited in any atom to having two electrons per orbital, right, because for any orbital we can either have a spin up electron, a spin down electron, or both.

这意味着在一个原子内,每个轨道上可以有两个电子，对吧，因为对任何轨道,我们可以有自旋向上或者自选向下或者两者都有。

麻省理工公开课 - 化学原理课程节选