Final answer:
The main cause of the movements leading to the Protestant Reformation was the corrupt practices of certain Catholic leaders, highlighted by Martin Luther's call for reform, which particularly contested the sale of indulgences and questioned Papal authority.
Step-by-step explanation:
One main cause of the reform movements that grew into the Protestant Reformation was the recognition that some Catholic leaders had utilized their power to engage in corrupt practices and amass wealth. This observation aligns with option C, emphasizing corrupt practices within the church as a significant impetus for reform. The dissatisfaction with these practices was notably expressed by Martin Luther, a German monk whose actions and writings, such as the posting of The Ninety-Five Theses on the door of a church in Wittenberg, catalyzed the Protestant Reformation. Luther and other reformers questioned the selling of indulgences and the authority of the Pope, advocating for faith alone as the path to salvation and scripture as the sole source of Christian authority. Although other factors influenced the launch and spread of the Protestant Reformation, such as the advent of the printing press and political dynamics, the desire to address and rectify ecclesiastical corruption was a central motivator of reform efforts.