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:
The main function of a fish's fins is to help the fish  
 (A) reproduce (B) see (C) breathe (D) move

Ex Output:
D


Ex Input:
A scientist combines oxygen and hydrogen to form water. This combination illustrates that water is  
 (A) an atom. (B) an element. (C) a mixture. (D) a compound.

Ex Output:
D


Ex Input:
Which form of energy is needed to change water from a liquid to a gas?  
 (A) heat (B) mechanical (C) chemical (D) sound

Ex Output:

A