What was significant about Pope Leo III's crowning of Charlemagne as emperor on Christmas Day, 800 CE?

a. This ceremony was the beginning of what would become known as the Holy Roman Empire.
b. Charlemagne could build a tremendous military force, because he had influence with the pope.
c. The crowning prepared Charlemagne to exert authority over papal decrees.
d. The crowning signaled that the papacy held more political power than Charlemagne did.

Answer: a