The following aquariums were set up with the same volume of water (elodea is an aquatic green plant)
aquarium 1: elodea only aquarium
2: elodea and an aquatic snail aquarium
3: aquatic snail only
which aquarium will establish a cycle of carbon dioxide and oxygen gas flow if placed in the dark for several weeks?

a. 1,2, and 3

b. 2 and 3

c. 3 only

d. none