ϸ, ġ ã ϴ. , Ѿ, ܶ, ã ƴϴ. ۵ ϱ , ϴ. EduLab ̾߱⸦ ϴ , å ȹϰ Ǿ. ְ ڷ̸鼭, ̾ ϰ, ϴ. , ̾ ε巴, зδ㵵 ٰ ִ. ̿ ߿ ϰ Ǿ, å <ְ ̱ >, <ְ 100> ϰ Ǿ. з, ý ø ǵǾ. ֱ å , , ִ. ̸ Ȱϸ ٷιٷ ã ְ, ܾ嵵 ִ.
1989 - George Bush
1993 - William J. Clinton
1997 - William J. Clinton
2001 - George W. Bush
2005 - George W. Bush
2009 - Barack Obama
2013 - Barack Obama