Which best explains the rise to power of Great Zimbabwe?

The choices can be found elsewhere and as follows:

A). Zimbabwe was a highly productive agricultural society.

B). Fish from Zimbabwe were a staple food of East African people.

C). Zimbabwe's military was stronger than others in the region.

D). Zimbabwe controlled the region's ivory and gold trade.

I believe the correct answer is the second option. A eason for great zimbabwe's rise to power would be that fish from Zimbabwe were a staple food of East African people.