Answer: Option C
Explanation:
The plants has the ability to survive on its own. It can itself release carbon dioxide into the closed system and use the carbon dioxide for the process of photosynthesis.
The snails in the aquarium plays a major role in the releasing carbon dioxide and cleaning the aquarium.
The ability of the plant to perform photosynthesis needs carbon dioxide and water and releases oxygen in atmosphere. Without snails also the plants will be able to survive on their own.