A more complete explanation is forthcoming, studyhelp, but while you're waiting for that I'll put this out there for you and others working through this question.
The passage is all about how Great Zimbabwe was able to achieve its size and success only because of its cattle-based agriculture. Throughout the passage we learn about how the cattle system required large-scale effort, central control, patronage, and a ruling class. Without all those factors at work, it simply couldn't have succeeded on a large scale due to the limitations of the savannah woodland environment.
I think the best support for the correct answer here is found in the very last sentence of the passage:
It was through its use of cattle as a powerful incentive to laborers that royalty was able to muster the human resources necessary for large-scale gold mining.
And that, of course, leads you to select answer D, which is the correct answer.
I hope that helps! We'll get a more complete explanation, including a look into why the wrong answers are wrong, soon!
Adam M. Tyson
PowerScore LSAT, GRE, ACT and SAT Instructor
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