Please choose the correct answer to the 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

Answer1: analyzing only melted ice cores. Answer2: analyzing more than one ice core. Answer3: comparing their data to the expected results. Answer4: comparing their data to modern pollution levels.

Answer format: answer1/answer2/answer3/answer4
Answer: answer2