Question

What distracted Emperor Charles V and Pope Leo X after 1521?

The Celtic threat to the northern border of the empire and the building of the Temple in Jerusalem.
The Muslim threat on the eastern border of the empire and the building of St. Peter's Basilica.
The Russian threat on the eastern border of the empire and the building of St. Peter's Basilica.
The Norse threat on the northern border of the empire and the building of Wartburg Castle.

Answer 1

The Muslim threat on the eastern border of the empire and the building of St. Peter's Basilica.

Charles V was preoccupied by the Ottoman (Muslim) threat and other external wars, while Pope Leo X was occupied with financing and overseeing the rebuilding of St. Peter’s in Rome.