But some of them may be the most difficult papers that you've written here.

但一些也许是你所写过的最困难的论文。

哈佛公开课 - 幸福课课程节选

I think the hardest part, it seems to me, of kind of, the elite universities in this country is getting in.

我想最困难的部分，在我看来，就是，要被这个国家精英的大学所录取。

对于赞助入学的看法 - SpeakingMax英语口语达人

And the toughest foreign policy issue?

那最困难的外交政策问题呢？

普林斯顿公开课 - 国际座谈会课程节选

It's, because sometimes it's generally tough at first,

学习语言最一开始的时候总会很困难，

想学会4种语言 - SpeakingMax英语口语达人

I think changing your mind is one of the hardest things.

我认为改变自己的思想是最困难的事情之一。

普林斯顿公开课 - 人性课程节选

There was a conditional agreement: yes, Norway should manage this oil risk but it's politically difficult and that's the problem-- is that we're not able to do our optimal management.

他们在一定程度上同意我的观点：,是的，挪威应该设法解决石油的风险,但这在政治上很困难,其问题在于-,挪威无法做到最优的管理。

耶鲁公开课 - 金融市场课程节选