Afghanistan's hot and harsh terrain can be hard on footwear.

VOA: standard.2010.07.06

For a couple of reasons. In some ways, this would be nicer, do expected cases, it's going to tell you on average how much you expect to take, but it tends to be hard to compute, because to compute that, you have to know a distribution on input.

关注最快的情况，在某种意义上来说，因为一些原因这样想挺不错的，当我们处理一个给定的问题,计算平均时间的时候,是很难计算的，因为你并不知道输入的分布情况,这些输入会是怎么样的呢？

麻省理工公开课 - 计算机科学及编程导论课程节选

And if they're a premade salad then it would be even more difficult because you're not constructing it yourself, so it's hard to uses based on these sort of things.

如果那是预制色拉,就更麻烦了,因为那不是你做的,就很难进行统计

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

This might be hard to do when the teacher is writing on a board at the front of the classroom.

VOA: special.2009.09.06

Now if all we have to go on is just this semiotic system, it's going to be kind of hard to put up resistance to by the same token we'll say "yellow" means "pause," "green" means "go."

而从语义学角度分析，我们必须不能这么想,这样绿色自然就表示继续，黄色表示暂停“

耶鲁公开课 - 文学理论导论课程节选

"We need leaders who are committed to moving New Jersey forward, (Applause) and that is John Corzine, which is why you need to work hard on Tuesday!" A Republican sweep will be seen by some as a rejection of President Obama's policies and could embolden Republican efforts to win congressional seats in 2010.

VOA: standard.2009.11.02