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.

Ex Input:
Which energy source is nonrenewable?  
 (A) sunlight (B) biomass (C) wind (D) fossil fuel

Ex Output:
D


Ex Input:
Which difference between water and ice results in ice floating on cold water?  
 (A) heat (B) shape (C) density (D) volume

Ex Output:
C


Ex Input:
After which event will ecological succession most likely happen?  
 (A) a forest fire (B) a thunderstorm (C) a high tide (D) a lunar eclipse

Ex Output:

A