Fact 1: Plants release oxygen during the day but not during the night.

Fact 2: Another kind of plant is the fishhook cactus.

Given the two facts above, answer the question "What does the fishhook cactus release during the day but not during the night." with the following options: 
- heat
 - Air
 - water
 - carbon monoxide
 - carbon dioxide
 - oxygen
 - Energy.
 - Energy


 

      oxygen   