Another problem is access. Connecting informal communities to the city's water pipeline is a challenge because many are living on the land illegally.

VOA: standard.2010.08.04

And scientists have been working on this for years and there's been progress, but it's still a very difficult challenge.

科学家们对此已经研究很久了,并取得了进展,但仍有很大挑战

耶鲁公开课 - 关于食物的心理学、生物学和政治学课程节选

For Garson,it has been a challenge to put aside his concerns about Haiti, and focus on football and the most important game of his career, but he has a simple message to Haitians.

VOA: standard.2010.02.04