Why is the answer not B?

Hi @Veda-Bhadharla, Thanks for the question! So remember, this is a main point question. Main point questions both have to be supported by the passage and actually be the main point (as opposed to some random thing the passage just mentions, for example). And an answer choice has to be completely correct; it can’t be 3/4 correct and 1/4 wrong. So keeping the in mind, let’s look at (B), which tells us that plants like maize that use a C-4 photosynthetic process have helped to shape the development of many human cultures, and this is because of their ability to produce greater quantities and higher qualities of nutrients. Are we told about getting greater quantities and qualities of nutrients? I don’t think the passage really mentions nutrients. It’s not because the crops themselves have more nutrients in them, it’s because there were just more of the crops themselves. So (B) gets that wrong about the passage, and so can’t be the main point. Hope this helps! Feel free to ask any other questions that you might have.