(C) It was using indulgences for financial benefits
Back in Martin Luther's time, the Church was the most powerful force in all the land. However, there was corruption in the Church, and they started selling "indulgences". Indulgences were payments made by ordinary people to the Catholic Church to be excused or exempted from penances for sin. Ordinarily, you go to confession, say your sins, and the priest absolves you, and gives you a few Hail Mary's and an Our Father to say as a penance (this is just an exaggeration, different penances come with different sins). Obviously, some people wanted to get off scot-free, and that's what these corrupt Church officials exploited.
As a result, Martin Luther wrote his 95 Theses, criticisms against the church, and placed it on the door of the church in Wittenburg. The printing press helped to distribute the 95 Theses much faster and to many different people. This ultimately led to many Europeans shedding their recognition of the Church's authority, and its fall in power.
