The researchers used an electron microscope and fossilized remains of thirty feathers that once covered the animal.

VOA: special.2010.03.16

I once counted the number of times he used the word the letter--O--in that poem, and I quit counting.

我曾经数过他到底在诗里用了多少个"啊",最后我放弃了

耶鲁公开课 - 美国内战与重建课程节选

n l m s Once we have chosen a certain mix of n, l, m and s, it is used once for that particular atom.

一旦我们选定了一组量子数，它就只能被一个固定原子所有。

麻省理工公开课 - 固态化学导论课程节选

Once growth is established, the box can be removed and used to start another planting.

VOA: special.2010.07.13

Once we sort of settle into this vocabulary, and once we get used to this clearly unquestioningly scientific perspective, why on earth do we need pseudo-statement or fiction at all?

一旦我们习惯了这种用语，一旦我们习惯了,这种科学视角，我们为什么还需要伪陈述和虚构呢？

耶鲁公开课 - 文学理论导论课程节选

The meetings used to be held about once every two years.

VOA: special.2009.06.03

She says the online tool was very effective for those who used it at least once a month.

VOA: standard.2010.07.30

"I think you get used to it after a while." "Once in a while it will get worse, so then it is a little bit nauseating, but it is actually fine, it is not too bad,I am used to it."

VOA: standard.2010.07.30