One, two, three, four, so on each level of the picture I'm drawing, I've seem only to be looking at each number once.

，2，3，4，可见，在我画的,这幅图的每一层上，对每个数字,都只会用到一次。

哈佛公开课 - 计算机科学课程节选

And not only was it a party school, you were going to have an amazing time for the four years and beyond.

不仅是个派对大学，而且未来四年甚至以后，都会过得很快乐。

哈佛公开课 - 幸福课课程节选

That makes sense because we know that every single electron has to have its own distinct set of four quantum numbers, the only way that we can do that is to have a maximum of two spins in any single orbital or two electrons per orbital.

那个讲得通,因为我们知道每一个电子,都有它自己独特的量子数,我们能做的唯一方式是,在任一单个轨道中最多有两个自旋电子,或者每个轨道有两个电子。

麻省理工公开课 - 化学原理课程节选

While there are only four different bases that make up either RNA or DNA, and so the complexity of an RNA polymer is limited.

在RNA或DNA的构成中,只含四种不同的碱基,因此一个RNA分子的复杂程度是有限的

耶鲁公开课 - 生物医学工程探索课程节选

Now remember that there were only four different colors in the cartoon of the DNA double helix that we talked about and I told you that those colors are really - represent the bases but there's five of them here.

现在要记住只有四种不同的颜色,在双螺旋DNA的卡通模型上出现,我们刚说过这个,我告诉你们的这些颜色,它们代表不同的碱基,不过有五种碱基

耶鲁公开课 - 生物医学工程探索课程节选