In his comments to the Middle Class Task Force, which is chaired by Vice President Joe Biden, Mr.Obama offered a preview.

VOA: standard.2010.01.25

Conversely, if I chose a Beta and my pair chooses an Alpha, so I end up with a C and she ends up with an A, then you know I have a bad time explaining to my parents why I got a C in this class, and I have to say about how I'm going to be president anyway.

相反如果我选β我对手选α,我得到C她得到了A,我回家后很难跟父母,解释为什么我只得到了C,然后我还得表示下雄心壮志

耶鲁公开课 - 博弈论课程节选

The president's message to students was simple: study hard,pay attention in class and embrace the opportunity to learn.

VOA: standard.2009.09.08

The president says the class of 2009 is leaving college at a time of economic uncertainty.

VOA: standard.2009.05.14

The president spoke at a meeting of a White House advisory panel set up to study the problems facing the middle class and propose solutions.

VOA: standard.2010.01.25

President Obama told the graduating class at Arizona State that what drives them through life should not be money, celebrity or power, but a higher calling.

VOA: standard.2009.05.14

President Obama said the current system has led the country to a breaking point, imposing hardships on middle-class Americans who struggle to pay for health care, who are unable to obtain it.

VOA: standard.2009.09.10