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.
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Question: Question: objects made of what cause refraction of light? Answer: melted sand.

Answer: objects made of glass cause refraction of light


Question: Question: Standing in a canyon and yelling your name? Answer: will cause your name to reverberate thru the canyon.

Answer: echo is when sound reflects off of a surface


Question: Question: the number of rings in a tree trunk can be used to estimate what? Answer: oldness.

Answer:
the number of rings in a tree trunk can be used to estimate the age of the tree