The correct answer is A) it sent Christian missionaries to help spread its faith.
The Byzantine empire spread Christianity in that it sent Christian missionaries to help spread its faith.
When Roman Emperor Constantine 1 moved the capital of the Roman Empire to Constantinople in Byzantium, he also took Christianity to the new place in 330 AD. Constantine had converted into Christianity in 312 AD. In the Council of Nicaea(modern-day Turkey), Constantine established Christianity as the official religion in the Roman Empire.