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What you've missed since London 2012

A lot has happened in the world of Olympic sports since the flame went out on the 2012 London Olympic Games. 

Michael Phelps retired ... and then he came back.

Usain Bolt was finally beaten -- by U.S. sprinter Justin Gatlin -- but he returned the favor at the 2015 World Championships.

After three consecutive beach volleyball gold medals alongside Misty-May Treanor, Kerri Walsh Jennings has a new partner as she eyes one more trip to the top of the medal stand.

American teenagers Simone Biles and Katie Ledecky emerged as the most dominant women in the world in their respective sports.

"Fierce Five" gymnasts Jordyn Wieber, McKayla Maroney and Kyla Ross called it quits on their professional careers, while London teammates Gabby Douglas and Aly Raisman came back to the sport with renewed vigor.

But if you want the full, unabridged guide to everything that's transpired in each summer Olympic sport over the past four years, read on below: