Priyanka took a destarched potted plant and set up an experiment as shown in the figure. She left the plant in sunlight for few hours and then tested the leaves X and Y for starch. Leaf X did not give starch test while leaf Y showed presence of starch. What is proved by this experiment?

• A. Chlorophyll is necessary for photo-synthesis.
• B. Carbon dioxide is necessary for photo- synthesis.
• C. Light is necessary for photosynthesis.
• D. Oxygen is given out during photo-synthesis.