Question

After the Roman Empire collapsed, the Catholic Church began to unify Europe by

taking on many duties of a government.
attracting many Christians.
letting people elect their own priests.
making the pope as powerful as an emperor.

Answer 1

After the Roman Empire collapsed, the Catholic Church began to unify Europe by taking on many duties of a government. 
So, the right answer will be the A taking on many duties of a government. 

Answer 2

A. taking on many duties of a government.