challenge: Which of the following mixes was used as a tutorial in the DJ Hero 2 demo?
  
  A. Lady Gaga featuring Colby O'Donis - Just Dance vs. deadmau5 - Ghosts N Stuff
  B. Pussycat Dolls featuring Busta Rhymes - Don’t Cha vs. Pitbull - I Know You Want Me (Calle Ocho)
  C. MSTRKRFT featuring N.O.R.E. - Bounce (Beat Juggle)
  D. Estelle featuring Kanye West - American Boy vs. Chic - Good Times
  Answer: 