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: When you make soap bubbles, what is inside the bubbles?  
 (A) Air (B) Soap (C) Water (D) Nothing
Example Output: A

Example Input: If the force used to push a shopping cart increases, the cart's acceleration will  
 (A) decrease (B) increase (C) remain the same
Example Output: B

Example Input: For his science project, Alan began a study of sugar maple trees. He noticed many differences among the sugar maple trees near his school. Which of the following three characteristics would vary the LEAST?  
 (A) height (B) number of leaves (C) type of seeds (D) trunk width
Example Output:
C