Detailed Instructions: You are given a science question (easy-level) and four answer options (associated with "A", "B", "C", "D"). Your task is to find the correct answer based on scientific facts, knowledge, and reasoning. Do not generate anything else apart from one of the following characters: 'A', 'B, 'C', 'D'. There is only one correct answer for each question.
Q: 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
(A) class discussion. (B) previous knowledge. (C) temperature changes. (D) student observations.
A:
D