When does the seventeenth episode of "The Simpsons"' twenty-first season which was renewed for by Fox aired?
American History X-cellent: "American History X-cellent" is the seventeenth episode of "The Simpsons"<nowiki>'</nowiki> twenty-first season and 458th overall. American History X-cellent:  It originally aired on the Fox network in the United States on April 11, 2010. The Simpsons (season 21):  It was the first of two seasons that the show was renewed for by Fox, and also the first season of the show to air entirely in high definition.
April 11, 2010