You are presented with the question "What does the fishhook cactus release during the day but not during the night." and the following answer choices: 
- heat
 - Air
 - water
 - carbon monoxide
 - carbon dioxide
 - oxygen
 - Energy.
 - Energy

Now knowing that plants release oxygen during the day but not during the night and another kind of plant is the fishhook cactus, choose the best answer.


 

      oxygen   