Explanation: Mali’s position below the Sahara desert meant that it was not easy for outsiders to conquer but because it sat astride the north-south trade routes to the Mediterranean it was definitely frequented by Muslim merchants. Eliminate (A) because the missionaries are coming from the wrong direction. Eliminate (C) because Berber tribes did not conquer Ghana. Eliminate (D) because Ethiopia and Mali were not rivals. Choice (B) is the best answer.