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 of the following best describes an advantage of using a mass production manufacturing system instead of a custom manufacturing system?  
 (A) Customers can provide specific feedback to workers. (B) Workers become skilled in all aspects of assembly. (C) Goods can be easily modified for customers. (D) Products can be made at a lower cost.
Example Output: D

Example Input: Which characteristic best identifies a pure substance?  
 (A) shape (B) texture (C) melting point (D) state of matter
Example Output: C

Example Input: If a species of bird stopped reproducing, which of these would happen?  
 (A) The bird's prey species would decrease in number. (B) The food web that the bird belongs to would collapse. (C) Trees where these birds build nests would grow taller. (D) This bird species would eventually disappear from nature.
Example Output:
D