kpop1-6, Exercise 3: Layers, foreign help and gaps

Model answer:

Earlier layers (any two): 1980s ballad singers such as Lee Gwang-jo and Byun Jin-sub ("Prince of Ballads"); Cho Yong-pil, whose repertoire included rock, dance, trot and folk-pop; 1990s hip-hop and R&B artists (Yoo Seung-jun, Jinusean, Solid, Deux, 1TYM, Drunken Tiger), following "I Know".
Foreign songwriters or performers (any one): will.i.am and Sean Garrett as songwriters/producers; Akon, Kanye West, Ludacris and Snoop Dogg as featured rappers.
Left out: song-writing camps and the verse-hook-drop structure, because the articles I read said nothing on them and no source was found, so writing about them would have been from memory.

Source: Wikipedia, K-pop (History, Characteristics).