Please choose the correct answer to the question: A student pours a clear liquid from a test tube into a beaker with a clear liquid already in it and notices that the mixture turns pink. The student infers the two clear liquids are different. This inference is a result of

Answer1: class discussion. Answer2: previous knowledge. Answer3: temperature changes. Answer4: student observations.

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