
The twin towers of the World Trade Center billow smoke after hijacked airliners crashed into them early 11 September, 2001.
NPR's Neal Conan talks with Rees, a Colorado State University history professor, about the difficult decisions he faces about when to stop teaching a piece of history, to make room for something new.
And teachers, tell us: As time marches forward, how do you make room for the new people and events that make up the recent past?
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