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

Fact 2: Plants include blue pine, hemlock, spruce and oak.

Given the two facts above, answer the question "What releases oxygen during the day but not during the night?" with the following options: 
- elephants
 - dogs
 - hydrocarbons
 - blue pine
 - Conifers
 - vegetation
 - humans
 - Fuel cells


 

    blue pine     