What are Islamic universities used for today?​

Indeed, all the answers are, to some extent, correct, but the most remarkable because it encompasses the reality of the other answers is  

B) his position as king of the Empire of Mali.

Explanation:

It is not possible to understand King (emperor) Musa's pilgrimage to Mecca without separating it from his status as the most powerful and richest king of his time.  

His abundant and very rich entourage, the fact that the pilgrimage lasted more than a year, the creation of a mosque every Friday throughout that same year, the establishment of trade routes and even the economic crisis that led to the Islamic holy lands due to the amount of gold he squandered among the needy, are some of the aspects derived from his condition, undisguised as the powerful king (emperor) of Mali.