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: When a cup of water at room temperature is put in a freezer, the water's state of matter will change from  
 (A) liquid to gas (B) gas to liquid (C) liquid to solid (D) solid to liquid
Example Output: C

Example Input: When iron combines with oxygen in a moist environment, rust forms because of a  
 (A) chemical reaction. (B) physical reaction. (C) change in density. (D) change in temperature.
Example Output: A

Example Input: Which part of the electromagnetic spectrum can humans sense without using equipment or technology?  
 (A) radio waves (B) visible light (C) microwaves (D) X-rays
Example Output:
B