What happens to the O2 and CO2 levels when one sprig of Elodea and one snail are put into a test tube with the lights on after 24 hours?
A: Drastic changes with oxygen increasing and carbon dioxide decreasing.
B: Drastic changes with carbon dioxide increasing and oxygen decreasing.
C: Oxygen and carbon dioxide vary slightly, but stay around their original levels.
D: There is no oxygen left in the test tube.
