analyzing only melted ice cores. analyzing more than one ice core. comparing their data to the expected results. comparing their data to modern pollution levels.
I gave my students this multiple choice question: Based on analysis of deep ice cores from the Arctic, scientists theorize that early humans caused air pollution. These scientists can make sure their data is correct by

Only one answer is correct among these 4 choices:
- analyzing only melted ice cores.
- analyzing more than one ice core.
- comparing their data to the expected results.
- comparing their data to modern pollution levels.

Could you tell me which one is correct?

analyzing more than one ice core.