Answer: C. Comparing plant growth under natural light, fluorescent light, and LED light
Explanation: We are searching for the experiment that is focused on studying the effects of different lights on plant growth. Thus, choice C is the best answer because it is the only answer choice that conducts an experiment comparing plant growth under different types of light. All of the other choices focus on studying the effects of other factors on other variables.
Choice A is investigating the effects of soil type and quality on plant growth instead of the effects of different light sources. Thus, it is incorrect.
Choice B is investigating how temperatures affect chemical reactions. It is neither investigating the effects of different types of light nor is it investigating how plant growth is impacted, so it is incorrect.
Choice D is incorrect because it is investigating the effects of pH levels on plant health. It is not investigating different types of light nor is it observing plant growth, so it is incorrect.