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.

Ex Input:
When a dog sees a cat, a message travels from the dog's eyes to the dog's  
 (A) brain (B) nose (C) paws (D) muscles

Ex Output:
A


Ex Input:
After a heavy rain, a mudslide flows into a pond and mud mixes into the water. Which of the following is most likely to happen?  
 (A) Fish will have more food. (B) Trees will be able to get more light. (C) Raccoons will not be able to find food. (D) Underwater plants will receive less light.

Ex Output:
D


Ex Input:
In which scenario below would natural selection most likely occur?  
 (A) centuries of gradual climate change (B) catastrophic destruction of habitat (C) rapid and profound climate change (D) immediate loss of primary food source

Ex Output:

A