One reason it's been harder to identify stem cells is that they're so rare; the other reason is that it's hard to identify the characteristics of them and it's taken many years to work this out.

干细胞难以识别的原因之一是,这些细胞很少,另一个原因就是,干细胞的特征性蛋白难以识别,我们花了好多年去解决这个问题

耶鲁公开课 - 生物医学工程探索课程节选

It's like rare, so everybody always go to the beach.

这么晴朗的日子不多见，每个人都会想去海边。

强力推荐 - SpeakingMax英语口语达人

It's about how so many plans in finance are messed up by rare events that suddenly appear out of nowhere.

书中提到金融界中突然出现的小概率事件,怎样搞砸了无数计划

耶鲁公开课 - 金融市场课程节选

These cells are rare and so it's been hard to identify them, that's part of it.

这些细胞太少了,所以很难找到,这是原因之一

耶鲁公开课 - 生物医学工程探索课程节选

So, it's pretty rare that chemistry makes the every day news.

通常化学不太会出现在日常生活新闻里。

麻省理工公开课 - 化学原理课程节选

So, if you by chance, I know it's very rare, but if by chance you don't get the class you can always follow up later.

如果你们偶然，我知道不太可能，但是如果不小心你们错过了某节课,你们就可以在之后补回来了。

麻省理工公开课 - 固态化学导论课程节选

But that is a terrible mistake because we should know that sculptresses are very rare; very few people have the job of a sculptress or sculptor, so it's a mistake.

但这是严重错误,我们都很清楚,雕刻家是很罕见的职业,只有很少人会是雕刻家,所以这是错的

耶鲁公开课 - 金融市场课程节选