Definition: 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.
Input: A student examined a rock sample and described it as having particles of various colors that were 1 millimeter to 12 millimeters in size. The student was making  
 (A) an inference (B) a hypothesis (C) a prediction (D) an observation
Output:
D