Final answer:
At Vézelay in July 1190, Richard I and Philip II agreed to reconcile their differences (Option D) to present a united effort in the reconquest of Jerusalem during the Third Crusade.
Step-by-step explanation:
At Vézelay in July 1190, Richard I of England and Philip II of France met to agree on the terms for their joint participation in the Third Crusade. While detailed specifics of their agreement aren't explicitly stated in historical records, it is understood that their meeting was to coordinate their efforts against the Muslim forces in the Holy Land, particularly focusing on the retaking of Jerusalem. After arriving in the Middle East, despite their intentions, it became evident that they managed to conquer various coastal territories but could not advance further inland due to internal squabbles and external resistance.
The answer to the question is that at Vézelay, Richard I and Philip II agreed to
reconcile their differences
(Option D) in order to present a united front in the Third Crusade. They aimed to combine their resources and forces to recapture Jerusalem, which had fallen under Muslim control led by Saladin. Their reconciliation was essential for coordinating the participation of European forces in the Crusade.
Following the Crusade, a treaty was eventually negotiated by Richard I, where Jerusalem remained under Muslim control, although Christian pilgrims were granted safe access to visit the city. This treaty with Saladin was one of the last Crusader successes in the Holy Land.