question: What sentence would provide a factual answer to this question: "Precipitation is when hail fall from clouds to the ground, and so is"

answer: precipitation is when hail fall from clouds to the ground

question: What sentence would provide a factual answer to this question: "objects made of what cause refraction of light?"

answer: objects made of glass cause refraction of light

question: What sentence would provide a factual answer to this question: "What would be a source of the smoothest rocks?"

answer:
contact between rocks over long periods of time causes rocks to smooth