In order for cells to produce the most energy, what gas should be present?

there’s no image attached but i can if you want: )

i think the answer would be d

fumikage isn't really a bird, and tsuyu does have teeth. tsuyu has a transformation quirk which still allows her to be partially human. otherwise we'd have a large frog running around. fumikage has teeth because again, he isn't a bird. his head was a quirk mixture if i'm correct.