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.