Answer: cause and effect
Explanation: Famed emperor Alexander the Great ordered his entire army to shave their faces and heads. This order was due to his belief that beards, and long hair made it easy for an enemy to grab and cut off a soldier’s head. But the key sentence was;
"This order was due to his belief that beards, and long hair made it easy for an enemy to grab and cut off a soldier’s head."
This shows that the answer is D, because it shows to tell why they had to cut and shave their hair and beards.