The two correct answers are:
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to offer evidence that insect populations have declined - The mention of suspiciously clean windshields and bikers less frequently swallowing bugs serves as anecdotal evidence that aligns with the study's findings about declining insect populations.
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to refer to an idea from paragraph 1 - The author brings back the idea of insect splatters mentioned in the first paragraph, linking it to the larger discussion about the decline in insect populations.