You are given a science question (hard-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 change is the best example of a physical change?  
 (A) a cookie baking (B) paper burning (C) ice cream melting (D) a nail rusting
Example Output: C

Example Input: Which characteristic applies to animals in only one of these taxonomic groups: reptiles, mammals, birds, amphibians, or fishes?      
 (A) have hair (B) lay eggs (C) have webbed feet (D) breathe with gills
Example Output: A

Example Input: Corn can be used to make ethanol, which is a fuel for some cars. What problem could be caused by the increased use of ethanol?  
 (A) increase in fossil fuel production (B) decrease in corn production (C) increase in severe weather (D) decrease in nutrients in soil
Example Output:
D

