Explanation?

Hi @kelsgorman, Thanks for the question! This question’s asking us for something that distinguishes the Ban Chiang populations in passage B from the populations discussed in the last paragraph of passage A. Well, what do we know about the populations in passage A, and the Ban Chiang population? Let’s start with passage A and go to the last paragraph. What are we told about the populations there? Well, we’re told that they’re nonagricultural but still have relatively high caries rates (lines 23-25). Now what are we told about the Ban Chiang? Well, we know that their diet includes cultivated rice and yams (lines 51-52)! In other words, that means that they had to have agriculture (because they cultivated the rice and yams, which is basically what agricultural is). And since they had agricultural, and the populations in passage A didn’t, answer choice (B) is correct. They ate cultivated foods, and the populations in passage A didn’t, since you can’t eat cultivated rice and yams if you don’t cultivate them. Hope this helps! Feel free to ask any other questions that you might have.

But in Passage A lines 16- 18 it talks about those "heavily dependent on CULTIVATED maize (a Zuni sample had 75 percent carious teeth). So how is (B) correct?

The question explicitly asks about the populations mentioned in the last paragraph of A. You need to read the question.