Orthodox christianity is predominant in what part of europe ?
a. southern europe
b. northern central europe
c. western central europe
d. eastern europe

Eastern Europe. The Great Schism in 1054 resulting in the splitting of the Catholic Church in Rome from the Orthodox Church in the Byzantine Empire. The Byzantine Empire occupied much of Eastern Europe, and the largest and most prominent country in Europe, Russia, was heavily influenced by Orthodox Christianity and the Byzantine Empire in general. Southern Europe and Western Europe remained highly Catholic, and after the Protestant Reformation, Northern central Europe became heavily protestant, especially Lutheran. 

The congress completes the diagram