What did the priest Johann Tetzel do that prompted Martin Luther to take action?

a. Tetzel sold Bibles printed in Latin.

b. Tetzel accused Luther of heresy

c. Tetzel challenged Luther to defend his 95 Theses in public

d. Tetzel sold indulgences, promising buyers an assured entry into heaven

The correct answer here is D. Johann Tetzel started selling indulgences Wittenberg to anyone who was be kind enough to donate the money for the reconstruction effort in Rome where they were rebuilding the Cathedral of St. Peter. This prompted Luther to nail his famous 95 Theses on the door of the Church in Wittenberg as Luther believed that faith alone is enough to grant salvation through Jesus Christ. This would later start the great wave of Protestantism.