Answer:
B. 2
Explanation:
Flask number 1 contains a plant, and plants uses carbon dioxide to make oxygen.
Flask number 2 contains 2 goldfish, and the more the organism the more the amount of CO2.
Flask number 3 contains a plant and 2 goldfish, The plant would use the CO2 creates from the fish to create oxygen, thus lowering the amount of CO2 in the flask.
Flask number 4 contains nothing, thus the about of Oxygen or CO2 inside the flask would remain the same.
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