Answer:
The correct answer is D) They rediscovered the learning of ancient Greece and Rome
Explanation:
At the time of the Crusaders the Muslim world enjoyed one of the highest living standards int he World. The Muslims were known for their high literacy rate, scientific and medical knowledge and being far more developed than Europe, which was the time, in it's dark ages.
The Muslims had also researched, codified and develop upon ancient knowledge of the Greeks and Romans. One positive aspect of the crusades was how this knowledge was transferred to Europeans and they rediscovered Greek and Roman literature.