Why does the professor mention $ 20 bill?

W: Do you like to run?
M: Yeah, when the Police are chasing me.
W: You know Kerron Clement?
M: Who?
W: (9) Kerron Clement. He just broke the world record in the 400-meter.
M: Right.
W: Did you know that he’s only 19 years old? Did you see it on the news?
M: I heard a hit about it.
W: Okay. Well, let’s look at the rest. (9) This Florida sophomore ran the 400-meter in 44.57 seconds at tile NCAA Indoor Track and Field Championships. He broke the mark of 44.63 seconds set by Michael Johnson in 1995.
M: (7)Hey, I’m fast. I could beat him any day.
W: (7) Yeah, only if there is a $ 20 bill blowing in the wind in front of you. Let’s get back to the story now. (10)Clement is from Trinidad and Tobago and moved to the United States when he was 13. He won the NCAA championship in the 400-meter hurdles and then won the world junior championship in the same event. At the junior championships, Clement competed for the United States after earning his U.S. citizenship last summer. He probably could have gone to the Olympics for Trinidad and Tobago last year, but preferred to become an American. Why do you think he wanted to become American?
M: Probably America is his new home and it has better living conditions than back home.
W: (8)Yeah, something like that. He said he loves competition and he wants to train with the best in the world, the Americans.