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:
When animals use energy, they produce  
 (A) nitrogen (B) iron sulfide (C) oxygen (D) carbon dioxide

Ex Output:
D


Ex Input:
A radio station broadcasting across a large area is experiencing thunderstorms. How will the radio waves from the station be affected?  
 (A) wavelength will be increased (B) amplitude will be unchanged (C) frequency will be distorted (D) speed will be decreased

Ex Output:
C


Ex Input:
A scientist crosses two different varieties of corn to produce a single variety that has traits from both parents. This technique is an example of  
 (A) competition (B) natural selection (C) selective breeding (D) ecological succession

Ex Output:

C