A newly released history of 20th Century Russia, written by a team of 45 scholars and edited by historian Andrei Zubov, includes a statement that much of the country's recent past is painfully difficult to study, which is why many refuse to do so.

VOA: standard.2009.12.25

But I want you guys to think about why it was difficult to do it another way, which is more pedestrian.

但是我希望你们能思考一下,为什么用另一种更普遍的方法来做,反而会比较难呢

耶鲁公开课 - 基础物理课程节选

Why is it difficult in some cases to produce a vaccine when we've been successful in so many others?

为什么某些疾病的疫苗很难研制,即使我们已经成功生产了很多种疫苗

耶鲁公开课 - 生物医学工程探索课程节选

I worked on specifically, I looked at -and this is also the reason why it's difficult to say what is a just university, because we didn't just look at Princeton, we didn't just look at Ivy League Schools or at least private institutions.

我专门研究的是,顺便，这也是为什么,为公正的大学下定义很难得原因，因为我们研究的不仅仅是普林斯顿大学，也不仅仅是常青藤学校,至少不是私人学校。

普林斯顿公开课 - 人性课程节选

And this is actually, in general, why it's sometimes difficult to teach or to tell stories because we constantly overestimate how much other people know.

概而论之，这就是为什么有时候我们很难能讲一个故事,因为我们总是认为别人什么都猜到了。

耶鲁公开课 - 心理学导论课程节选

But before telling you about this let me sort of Go through some of the hypothesis that we have and That we are now testing about why the subject is Difficult and why these materials assembled what We have assembled them might be useful.

但是谈那之前我要说说,我们之前的一些假设,我们现在正在测试为什么这个学科很难,以及为什么我们整合这些资料是有用的,我们认为把它们整合起来或许有用。

麻省理工公开课 - 媒体、教育、市场课程节选

Why is this a more difficult game to attain coordination in?

为什么这个博弈更难协调

耶鲁公开课 - 博弈论课程节选

Now the question is "how does it expand" and "why is it so difficult for us to understand, accept, assimilate and live according to the fact that we can make a difference, if we understand that what we need to understand is how change happens.

问题是“它如何扩大“,以及为什么我们难以理解，我们能够做出改变这个事实,并接受，被同化以及据此生活，如果我们能了解我们需要理解的,是改变如何发生。

哈佛公开课 - 幸福课课程节选

Why is this a slightly more difficult game?

为什么这个博弈更难一些呢

耶鲁公开课 - 博弈论课程节选