Answer: C, The introduction of Germanic tradition into the Western church.
Short answer: I took a test with the same question.
Long answer: A big problem for the Christian church were disagreements over the use of icons.
Primary language was also a big problem for the church.
To add to that, there were also disagreements over the rights of clergy members.
So, the only logical answer would be C, the introduction of Germanic traditions into the western church.
Hope this helps! :)