Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: Matter that mechanical wave energy can only travel through is medium.

A: What is the name of matter that mechanical wave energy can only travel through?
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Q: The sun is considered the center of the solar system.

A: What is considered the center of the solar system?
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Q: Test wells are drilled to monitor groundwater pollution.

A:
What are drilled to monitor groundwater pollution?
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