Final answer:
The main reason for the mutual hatred between Christians and Muslims was b. religious intolerance.
Step-by-step explanation:
The main reason for the centuries-long mutual hatred between Christians and Muslims was b. religious intolerance. Throughout history, religious differences and a lack of acceptance of other faiths have led to conflicts and bloodshed between these two religious groups.
The Crusades serve as a prime example of how religious intolerance fueled violence, as Christian armies aimed to recapture Jerusalem from Muslim control.