The heavy oxygen isotope (18O) could be provided to plants either in the CO2 or in H2O or in both. Today, we know from experimental results that O2 released from chloroplasts comes from H2O and not from CO2. Which of the following experimental results would show conclusively that O2 is released from H2O and not CO2?

A. When heavy oxygen is part of water given to the plant, the plant produces heavy O2.
B. When heavy oxygen is part of both water and CO2 given to the plant, the plant produces heavy O2.
C. When no heavy O2 is part of water given to the plant, the plant produces no heavy O2.
D. When no heavy oxygen is part of CO2 given to the plant, the plant produces no heavy O2.