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 of these determines whether a fertilized egg develops into a toad, a snake, or a lizard?  
 (A) the sex of the egg (B) the age of the egg (C) the size of the egg (D) the genes of the egg
Example Output: D

Example Input: The fur of some animals becomes thicker in the winter and is shed in the spring. These observations show how animals  
 (A) respond to changes in the environment (B) move from place to place to survive (C) store fat for the winter (D) compete with other animals for food
Example Output: A

Example Input: Which comparison of ecosystems is true?  
 (A) Tundras are warmer than grasslands. (B) Grasslands get more rain than deserts. (C) Deserts have more plants than rainforests. (D) Rainforests are rockier than tundras.
Example Output:
B