instruction:
In this task, you are given a question and a corresponding answer. Your task is to generate a fact statement that is useful in answering the given question.
question:
Question: objects made of what cause refraction of light? Answer: melted sand.
answer:
objects made of glass cause refraction of light


question:
Question: Where would rocks be the smoothest? Answer: where water has flowed for years.
answer:
contact between rocks over long periods of time causes rocks to smooth


question:
Question: An early example of harnessing wind power would be? Answer: cloth on masts.
answer:

wind is a source of energy