What were two important uses of sheep in mongolias nomadic economy prior to the rise of genghis khan?

a. sheepskin was used for trade, and sheep wool was used to make tents.

b. sheep milk was used for food, and sheepskin was used to make clothing

c. sheep were traded for gold, and sheep meat was an important food source.

d. sheep were used as a currency, and sheep wool was used as a food source.