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: Which physical structure would best help a bear to survive a winter in New York State?  
 (A) big ears (B) black nose (C) thick fur (D) brown eyes
Example Output: C

Example Input: Some events on Earth happen instantly while others take thousands of years to occur. Which process takes the longest time to complete?  
 (A) rivers rising due to storms and floods (B) evaporation of water from the leaves of a plant (C) weathering of a rock to form small rocks and sand (D) movement of small pieces of rock by flowing water
Example Output: C

Example Input: Oxygen-rich blood returns from the lungs to the heart. Which two systems are most directly involved in this process?  
 (A) excretory and digestive (B) circulatory and excretory (C) digestive and respiratory (D) respiratory and circulatory
Example Output:
D