Which event occurred soon before the Great Schism of 1054 and helped cause the event? A
Pope Urban II authorized a disastrous expedition to conquer Jerusalem.
B
Pope Clement V moved the seat of the church's power from Rome to Avignon.
С
Pope Leo IX and Patriarch Michael Cerularius excommunicated each other.
D
Pope Leo X ordered the sale of indulgences to fund repairs of St. Peter's Basilica.
U

C. Pope Leo IX and Patriarch Michael Cerularius excommunicated each other

Explanation:

The Great Schism refers to the  break of communion between the Roman Catholic  and the Orthodox. Mostly happen because of the fight for authority and difference in some key religious teachings. (for example, Roman Catholics require the priest to be celibate while the Orthodox allowed married Clergy)

The situation escalated after  Cartularies (prominent figure in the Orthodox) and Pope Lex IX (prominent figure in the Roman church) excommunicated one another due to this difference. Compromise was very unlikely to happen since both of them sincerely believed that they represented the right interpretation of God's teaching.

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