Question

How did camels help increase trade across geographic barriers of northern africa

Answer 1

Camels carried heavier loads and traveled far without water. Hence, Option C is the answer you seek. :D

Answer 2

the way that camels help increase trade across geographic barriers of northern Africa is : Camels helped with transportation.
Back then, we still have not developed machine based transportation vehicles, so we rely on ships and carts. Since the horses are unable to cross pass the desert, most of the animals that is used on northern Africa trade were camels.