Why Did the Researchers Keep Carbon Dioxide Levels Constant While

Multiple Choice

Why did the researchers keep carbon dioxide levels constant while they varied oxygen levels and then keep oxygen levels constant while they varied carbon dioxide levels?

A) It is technically easier to vary the level in the water of one gas at a time.
B) They could only measure the level of one gas in the water at a time.
C) The effects of oxygen and carbon dioxide levels could interact.
D) Only one gas at a time varies in estuaries in the summer.