Question: What is this South Korean-Chinese boy group formed by S.M. Entertainment in 2011 initially with several members and broke up a year later that released the song "Mama" in 2012?
Sentence (from "Exo videography"): Separated into subgroups EXO-K and EXO-M, respectively performing music in Korean and Mandarin, the band debuted on April 8, 2012 with the single, "Mama".
Relevant evidence: No