question: What American animated sitcom had it's twenty-first season air on Comedy Central?
answer: South Park
context: Title: 2017 Air Force Central F.C. season
  Passage: The 2017 Air Force Central F.C. season was Air Force Central's 12th consecutive season in the Thai League 2.  This season Air Force Central participate in the Thai League 2, FA Cup and League Cup
  Title: List of Futurama episodes
  Passage: The American animated science fiction sitcom "Futurama", created by Matt Groening for the Fox Broadcasting Company, aired on Fox from March 28, 1999, to August 10, 2003; Cartoon Network's Adult Swim aired reruns of the show from 2003 through 2007.  Following a commitment from 20th Century Fox Television to produce four straight-to-DVD "Futurama" films, Comedy Central announced on June 23, 2006 that they were resurrecting the show and would air the films as new "Futurama" episodes (reconfiguring each film into four episodes) after each film's DVD release.  Comedy Central began airing "Futurama" reruns in January 2008 and broadcast on March 23, 2008.  Following the four films (considered the fifth season of the show), Comedy Central has broadcast a sixth season of twenty-six episodes, split over 2010 and 2011.  A seventh season was announced in March 2011 and debuted in the summer of 2012.
  Title: South Park (season 15)
  Passage: The fifteenth season of the American animated sitcom "South Park" began airing on Comedy Central on April 27, 2011 and ended on November 16, 2011.  In response to reactions to the mid-season finale episode "You're Getting Old", which seemed to insinuate that creators Trey Parker and Matt Stone were wrapping up the series, Comedy Central proclaimed through the media that "South Park" was renewed for two more seasons, and the duo were signed through 2013.  Shortly before the airing of the season finale episode "The Poor Kid", "South Park" was extended again until 2016, taking the show to 20 seasons.  Parker was the director and writer for all episodes, and Robert Lopez was the writer in this eleventh episode for the fifteenth season.
  Title: Yo Leela Leela
  Passage: "Yo Leela Leela" is the twenty-first episode of the sixth season of the animated sitcom "Futurama".  It aired on Comedy Central in the United States on July 21, 2011.  The title is a reference to the Nickelodeon kids' show "Yo Gabba Gabba! ".  The show is also parodied within the episode: Leela's show is similar, featuring people dressed up in fanciful costumes as its main characters.
  Title: Assie Come Home
  Passage: "Assie Come Home" is the twenty-first episode of the seventh season of the animated sitcom "Futurama".  It originally aired on Comedy Central on July 31, 2013.  The episode was written by Maiya Williams and directed by Raymie Muzquiz.  Bender searches the universe for his shiny, metal ass after an alien street gang has him stripped down to his bulb eyes and mouth grille.
  Title: Holiday Special (South Park)
  Passage: "Holiday Special" is the third episode in the twenty-first season of the American animated television series "South Park".  The 280th episode of the series overall, it first aired on Comedy Central in the United States on September 27, 2017.
  Title: White People Renovating Houses
  Passage: "White People Renovating Houses" is the first episode in the twenty-first season of the American animated television series "South Park".  It is the 278th episode of the series overall, and first aired on Comedy Central in the United States on September 13, 2017.
  Title: South Park (season 21)
  Passage: The twenty-first season of the American animated sitcom "South Park" premiered on Comedy Central on September 13, 2017, and will contain ten episodes.
  Title: Put It Down (South Park)
  Passage: "Put It Down" is the second episode in the twenty-first season of the American animated television series "South Park".  The 279th episode of the series overall, it first aired on Comedy Central in the United States on September 20, 2017.
citations: Put It Down (South Park) South Park (season 21)