Definition: Given a scientific passage and an answer, generate a question for the given answer.
Input: Passage: In biological systems, matter is continuously changing states as well. For example, carbon in the form of the gas carbon dioxide is changed into glucose, a solid. This change, of course, occurs during photosynthesis. During cellular respiration, carbons from the glucose molecule are changed back into the carbon dioxide gas. Answer: carbon dioxide
Output:
During cellular respiration, carbons from the glucose molecule are changed back into what gas?