It can be assumed that the Mali referred in the question refers to the Mali Empire, which was located in West Africa and its dominion spans from the Atlantic Coast to the central parts of the Sahara Desert. The empire was around from the 13th century to the early 17th century. In contrast, the Kingdom of Axum is located in today’s northern Ethiopia and Eritrea and its establishment was around from the 100 to 900 AD.
The main difference between the two is that (B) Mali became primarily a Muslim culture.