The White House says President Barack Obama will attend next month's climate change summit in Copenhagen,Denmark, and will make a provisional pledge to cut U.S.greenhouse gas emissions by 17 percent from 2005 levels by 2020.

VOA: standard.2009.11.26

So, I make a pledge. You give me seven hours a week, you will pass this class, not just by the skin of your teeth. You will pass it.

我保证，你们要是一周学习7个小时，肯定可以通过这门课，一点都不惊险，你们会通过的。

麻省理工公开课 - 固态化学导论课程节选