You're Conducting an Experiment to Determine the Effect of Different

You're conducting an experiment to determine the effect of different wavelengths of light on the absorption of carbon dioxide as an indicator of the rate of photosynthesis in aquatic ecosystems. If the rate of photosynthesis increases, the amount of carbon dioxide in the environment will decrease, and vice versa. Small aquatic plants are placed into three containers of water mixed with carbon dioxide. Container A is placed under normal sunlight, B under green light, and C under red light. The containers are observed for a 24-hour period.
-Carbon dioxide absorption is an appropriate indicator of photosynthesis because

A) CO₂ is needed to produce sugars in the Calvin cycle.
B) CO₂ is needed to complete the light reactions.
C) plants produce oxygen gas by splitting CO₂.
D) the energy in CO₂ is used to produce ATP and NADPH.