Thanks for the question! Let’s take a look at the first paragraph. The first paragraph talks about the cultivation of maize, also known as corn, and its sheer productivity. The passage does also bring up “a few similar crops” in line 15, as well as a group of plants called C-4 plants in general (including sugar cane and rice in the last few lines). But it’s clear that the focus of the passage is on “maize’s impressive productivity” (line 18), and maize is the focus of the introductory paragraph. Thus, when (B) states productivity of a particular crop, it’s referring to maize, and this is consistent with the contents of the passage. Hope this helps! Feel free to ask any further questions you might have.