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: Some people carry a mutated allele of a particular gene that makes them resistant to HIV infection and AIDS. Which best describes this type of mutation?  
 (A) beneficial (B) asexual (C) harmful (D) unicellular
Example Output: A

Example Input: Which part of an atom is involved in chemical reactions?  
 (A) nucleus and its particles (B) negatively-charged particles (C) neutrally-charged particles (D) positively-charged particles
Example Output: B

Example Input: When trees develop leaves in the spring, 10 changes occur on the forest floor. Why does the development of leaves cause changes on the forest floor?  
 (A) Rainfall increases. (B) Sunlight is reduced. (C) Wind speed increases. (D) Animal migration is stopped.
Example Output:
B