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: India is in the Northern Hemisphere and Australia is in the Southern Hemisphere. In June, it is summer in India and winter in Australia. What is the main reason the seasons are opposite in the two countries?  
 (A) because Earth is tilted on its axis (B) because the Sun rotates on its axis (C) because Earth revolves around the Sun (D) because of the distance between the countries
Example Output: A

Example Input: Which of the following would be more likely to pollute a river?  
 (A) allowing beavers to build a dam (B) spreading fertilizer near the river (C) mowing the grass on the river bank (D) fishing from a bridge over the river
Example Output: B

Example Input: Which body system is most responsible for the removal of waste?  
 (A) skeletal system (B) nervous system (C) muscular system (D) excretory system
Example Output:
D