2. David is growing algae in a closed bottle for an experiment. The bottle is half full of water and half full of air. David floats the bottle in a pond for three weeks. At the end of the three weeks, David notices that lots of algae grew, but the bottle did not sink lower in the pond.

Why didn't the bottle of algae get heavier during the experiment?

A. Tiny animals in the bottle ate the growing algae.

B. The sides of the bottle got lighter as the plastic degraded.

C. The bottle has a leak, which made it lose water to the pond.

D. The growth of the algae came from the air and water in the bottle.