The correct answer is C) Henry IV believed he had the authority to appoint church officials
In the 11th century, Pope Gregory VII started a Reform in the Church with the goal of increasing his political power. This reform was based on the idea that the Pope was not only above every bishop and the local churches, but also every prince and even the emperor of the Holy Roman Empire were subjected to the ecclesial authority. This reform undermined the power that the Emperor had until then of appointing church officials and bishops, and since the Emperor Henry IV was not willing to lose that power, a long conflict between both authorities took place.