As far as the first option is concerned, it did not contribute to the fact that Christianity was acting as a unifying force, because it was a conflict on the soil of Europe, so it could only have an unbalance. Signing Magna Carta also led to the conflict between the opposing sides, the king and the nobility, which means it is not unifying. The Shism in the Christian Church can unite one against the other, ie the East against the West and does not mean the unification of the Christian force on the ground throughout Europe, although in that sense there was no significant conflict except at the political, theoretical and spiritual levels.
What truly united Christianity to act as a uniting force in Europe is the struggle against the Islamic expansion, it has even been noted that the Crusades, in their campaigns, made alliances with some Eastern countries and had military assistance.
The answer is: d.
