Which statement about the Sahara is most closely

associated with the West African civilizations of

Ghana and Mali?

(1) Irrigation systems made it possible to farm in

the Sahara.

(2) Salt mined in the Sahara was exchanged for

gold.

(3) Oases in the Sahara served as their capital

cities.

(4) The Sahara prevented the spread of Islam to

the region.