Please choose the correct answer to the question: As an airplane climbs in the sky, the pilot notices ice crystals forming on the windshield. This happens because

Answer1: blizzards occur more often at higher altitudes. Answer2: friction with the atmosphere causes ice to develop. Answer3: water evaporates faster at higher altitudes, resulting in ice crystals. Answer4: moisture on the outside of the plane freezes due to colder air at higher altitudes.

Answer format: answer1/answer2/answer3/answer4