The Nomadic Horsemen of Central Asia Had What Crucial Advantage

The nomadic horsemen of central Asia had what crucial advantage when interacting with other peoples?

A) They developed superior bridles and yokes to aid horses in transporting goods.
B) They had unique knowledge of the mountain passes through which trade goods flowed.
C) They developed political ties with dozens of local kings who allowed them to carry trade goods.
D) Because of their mobility, they had acquired resistance to many diseases.