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:
Manuel wants an area in the yard to wash the dog without making mud puddles. He wants to put something on the ground that water passes through easily. Which of these materials would be the best for him to use?  
 (A) clay (B) plastic (C) soil (D) pebbles

Ex Output:
D


Ex Input:
Which of these most likely determines if a mutation will become an adaptation in a species?  
 (A) genetic variation (B) mitosis (C) natural selection (D) succession

Ex Output:
C


Ex Input:
Which action would increase the amount of oxygen in a fish tank?  
 (A) adding more fish (B) adding more plants (C) placing food in the tank (D) placing a water heater in the tank

Ex Output:

B