"Tea is the world's second most popular drink, second to water, and there are literally thousands of tea formulations around the world, so the challenge for us, isn't finding new tea recipes, it's focusing and making sure we're developing things that are going to work."

VOA: standard.2010.02.17

Realize that there's an inevitably challenge for us and actually helping people in this kind of context, especially as the deadline really approaches.

这对我们来说是一个不可避免的挑战,需要在这种环境下帮助人们，特别是当最后期限要接近了。

哈佛公开课 - 计算机科学课程节选

So I think that it's true that the economy is difficult and there is big challenge in front of us.

所以我觉得，目前的经济形势真的很困难，我们面临着很大的挑战。

事业就是挑战 - SpeakingMax英语口语达人

And the challenge then is, for us, if our goal is to become practical idealists is to understand what it is that brings about change and then do it.

困难在于，如果我们想成为实践理想主义者,就要理解是什么带来改变然后去做。

哈佛公开课 - 幸福课课程节选

Now that's not a very realistic assumption and we are going to come back and challenge it at the end of semester, but this will be complicated enough to give us a lot of material in the next ten weeks.

这不是一个很符合实际的假设,在期末的时候我们再来推翻这个假设,但是就这个假设下的内容,就足够我们接下来的十个星期学的了

耶鲁公开课 - 博弈论课程节选