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.

Example Input: What is the primary function of white blood cells in humans?  
 (A) carry oxygen (B) fight disease (C) grow tissues (D) remove waste
Example Output: B

Example Input: Energy appears in many forms. What form of energy is lightning?  
 (A) electrical energy (B) mechanical energy (C) magnetic energy (D) sound energy
Example Output: A

Example Input: A student pours water into a cup and places the cup in a freezer. After many hours, the water will change from  
 (A) solid to gas (B) solid to liquid (C) liquid to solid (D) liquid to gas
Example Output:
C