Here's a problem to solve: A scientist put several different plants in a sealed container. Every hour, she checked the oxygen in the container to see if it changed. How did the oxygen in the container most likely change?

Among the 4 following options, which is the correct answer?

- A: The amount of oxygen increased.
 
- B: The amount of oxygen decreased.
 
- C: The oxygen was transformed into water.
 
- D: The oxygen was transformed into carbon dioxide.
 