A scientist publishes a paper that states that changes in the levels of gases in the atmosphere of a moon of Saturn indicate that there may be extraterrestrial life on that moon. Which statement correctly answers whether the question of alien life on this moon is scientific?

A question is scientific when evidence can be gathered to test it and the results can be checked by others. The claim about atmospheric gas levels can be investigated through observations and measurements, so the question of whether those changes indicate life is testable and verifiable. Therefore, choice D is correct.

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