What was the primary basis of aksum's wealth?

It seems that you have missed the given choices of the question above; but anyway, here is the correct answer. The primary basis of Aksum's wealth is that, they controlled extensive trade routes that connected many cultures.

Here are the given choices:

A They discovered rich gold deposits within the boundaries of the kingdom.

B They controlled extensive trade routes that connected many cultures.

C They exported thousands of slaves to Europe.

D They conquered Egypt and assimilated all of Egypt's wealth.