Cyril and Methodius:.
A) Converted many of the Slavic tribes to Christianity
B) Were the first great rulers of Kievan Russia
C) Were the originators of the iconoclast controversy in Byzantium
D) Were responsible for the schism of 1054 between the Latin and the Greek churches

Converted many of the Slavic tribes to Christianity

Explanation:

Cyril and Methodius converted many of the Slavic tribes to Christianity

Cyril  (827-869)and Methodius (825-885) now Saints were brothers, theologians and missionaries. They were known for their work in evangelizing the Slavic tribe (preaching Christianity in the native language which brought the countries firmly to Christianity)and influencing the religious and cultural development of all Slavic peoples . They also helps to invent the Galgolitic and Cyrillic alphabets which are the oldest known Slavic alphabet, which helps in translating the Bible and other texts into Slavic language

A is correct (Converted many of Slavic tribes to Christianity)

Explanation: they arrived to Great Moravia (first medieval state of western Slavs whose center was situated in today´s south Moravia; its territory covered part of today´s Slovakia, the Czech rep., part of Poland and Hungary) and brought there Christianity. Later this sort of Christianity was transferred from south Moravia to central Bohemia (where settlement of what is Prague today was situated) where they converted first Premyslids (first Bohemian ruling dynasty): duke Borivoj and his family (duke´s wife Ludmila became the first Czech saint). Great Moravia was ruled by so-called "Mojmir dynasty" and was destroyed by Hungarian (Magyar) tribes at the beginning of the 10th century. Mission of Cyril and Methodius was an answer to demand of Great Moravian Duke Rostislav I. who (in 860) asked pope Nicolas I for "teachers". Christianity was entering to Great Moravia not only from the east but also from the west. Later on western influence prevailed.

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