Which of the following observations would support the claim that as plants absorb sunlight to make food they release oxygen into the environment?
A. Oxygen concentration in the atmosphere was much higher millions of years ago when different plans existed.
B. When plants are kept in skilled environment the concentration of carbon dioxide steadily goes down.
C. Plants that are kept under conditions of total darkness want to grow normally and eventually will die.
D. The oxygen concentration in a pound with many plants increased during the day and decreases at night and on cloudy days.
Please help