Became the first christian emperor.
a. constantine
c. cicero
b. nero
d. julius caesar

Constantine became the first Christian emperor.

Constantine was a Roman emperor who transformed to Christianity. He also acknowledge religious ability to every district in the empire. Being a saint in the Eastern and Oriental Orthodox Church, Constantine was later baptized before his afterlife. 

Constantine- there's a story about how he converted when he saw a cross during a battle- he ended winning the battle, saw the cross as a sign, and so converted.