The breakup between the Western Catholic and Eastern Orthodox Church already occurred gradually over the centuries, in order to escalate into a split in 1054. There were political and religious reasons that led to it. From the religious issues that led to the dissolution of the Western and Eastern Church leaders, it was learning about whether the Holy Spirit came from the Father or from the Father and from the Son. Also, one of the religious issues was whether the priests should be allowed to get married or not.
It should be emphasized that there has never been a dispute between the West and the East, whether it is necessary to believe in more than one God, both of them argued that God is only one.
the third option offered, about the discussion of the divine nature of Jesus, was the subject of discussion earlier in the Church Councils, but did not directly affect the breakup of the church
According to your options, the correct answer is: whether priests should be allowed to get married.