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 example would result in new cells that are most different from the parent cells?  
 (A) yeast cells splitting into new cells (B) bacteria cells dividing into new cells (C) skin cells dividing to produce more skin cells (D) sperm and egg cells uniting to produce fertilized egg cells
Example Output: D

Example Input: The floating arrow on a compass always points towards the  
 (A) west. (B) east. (C) south. (D) north.
Example Output: D

Example Input: Which human organ system exchanges gases with the environment?  
 (A) endocrine (B) circulatory (C) respiratory (D) integumentary
Example Output:
C