Strongly supported. The unusual productivity of C-4 plants, as compared to many other plants, is the result of rubisco's isolation in airtight tissues in the center of the leaf. This prevents oxygen gas from interfering with with rubisco, while in other, less-productive, non-C-4 plants, we know that oxygen does interfere with rubisco. We can infer that non-C-4 plants therefore don’t isolate rubisco from oxygen the way C-4 plants do.

Misdirection. C-4 molecules contain four carbon atoms. The author doesn’t discuss rubisco’s chemical composition.

Unsupported. Rubisco’s role is to assist carbon dioxide in building sugars (which are presumably nongas molecules), but we don’t know whether rubisco directly converts carbon dioxide into anything. Also, while rubisco is important and helpful to this process, we don’t know if it’s strictly necessary. (C) is also pulling a misdirection: in C-4 plants, carbon dioxide must first be converted to a nongas molecule before it can react with rubisco. (We’re never told what coverts carbon dioxide into that nongas molecule.)

Misdirection. Rubisco is the target of oxygen buildup, in maize or any other plant. Oxygen binds to rubisco, which has the detrimental effect of preventing rubisco from properly carrying out its role in photosynthesis. In maize, through, bundle sheath cells are there to help protect rubisco from the detrimental effects of oxygen buildup.

Unsupported. The author does touch on the effects of increased oxygen levels in P2, but she says that increased oxygen has a negative effect on rubisco—and she’s talking about non-C-4 plants. In the C-4 process, meanwhile, oxygen is kept away from rubisco altogether. There’s no indication that the C-4 process improves when the ratio of oxygen to carbon dioxide is high. If anything, we should expect that things improve when there’s a low ratio of oxygen to carbon dioxide, because that means there’s relatively more carbon dioxide to fuel the photosynthesis reactions that rubisco helps with.