Students are observing an aquatic plant. They understand that the bubbles they see rising from the cut stem of the plant are the gases produced during photosynthesis. Which of the following observations provides the best evidence that light is the source of energy for photosynthesis? A Plants observed in artificial or in natural light were both seen to produce bubbles. B The frequency of bubbling increases in bright light and slows to a stop in darkness. C The orientation of the light seems to have no effect on the production of bubbles. D The bubbles always rise to the surface of the water, moving towards the light.