Final answer:
Isaac Angelus did not make a specific agreement to slow the crusaders according to the information provided. The most relevant agreement affecting Crusader progress was the Treaty of Jaffa, made by Frederick II, which favored diplomacy over military action and resulted in a truce with Sultan al-Kamil. The correct option is A.
Step-by-step explanation:
The agreement made by Isaac Angelus that slowed the crusaders was not mentioned explicitly in the provided information. However, the closest event we can infer from the given context was the Treaty of Jaffa, by Frederick II, not Isaac Angelus.
Frederick II made an agreement with Sultan al-Kamil in 1219, which led to slowing the Crusaders' progress towards military conquest and instead favored diplomatic resolutions.
This treaty offered a peace between Christians and Muslims, allowing Frederick to be the titular king of Jerusalem with limited power, but kept the city defenseless without walls and kept important Islamic holy sites under Muslim control.
Other delays mentioned in the information that impacted crusaders include the diversion of the Fourth Crusade to Constantinople to enforce a power change, and the financial issues that arose when the Byzantine allies could only provide half the promised money in support of the crusaders. The correct option is A.