You are given a science question (hard-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.

Example Input: What part of the digestive system first causes chemical changes to food?  
 (A) teeth in the mouth (B) saliva in the mouth (C) enzymes in the stomach (D) enzymes in the small intestine
Example Output: B

Example Input: A student pushed a large rubber ball on a flat, frictionless surface. The ball rolled at a speed of 1 meter per second. Which statement best describes the motion of the ball when the student stopped pushing the ball?  
 (A) The ball accelerated. (B) The ball did not move. (C) The ball changed direction. (D) The ball continued to move in the same direction.
Example Output: D

Example Input: A student gives a red toy car a push on a wooden floor. The student then pushes the same red toy car on a cement floor. Which question is the student most likely investigating?  
 (A) How fast does a toy car usually roll? (B) What is the best way to make a toy car roll? (C) Which surface allows a toy car to roll farther? (D) Does color have an effect on the distance a toy car rolls?
Example Output:
C