challenge: With whom did Emil Kostadinov form a successful trio at CSKA Sofia in the late 1980s?
  
  A. Hristo Yovov and Petar Zhekov
  B. Hristo Stoichkov and Luboslav Penev
  C. Dimitar Penev and Nasko Sirakov
  D. Georgi Dimitrov and Ivan Petrov
  Answer: 