The correct answer is D. The missionary brothers who converted the Slavic peoples of Moravia to the Orthodox Christianity of the Byzantine Empire were Cyril and Methodius.
Explanation:
Cyril and Methodius were two brothers born in the 8th century in Thessaloniki who became missionaries of Christianity in the Khazars and Moravia. They promoted the use of the Old Church Slavonic as a liturgical language and developed the Glagolitic alphabet, the predecessor of the Cyrillic alphabet.
In fact, the nickname of Cyril was Constantinos, and he worked as a philologist and university teacher in Constantinople. The original name of Methodius has still not been found out, but he was a monk and at some point in his life also worked as an administrator.
