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:
One substance found on Earth is more stable as an elemental gas than as part of a solid compound. As a result, this substance is very abundant in the atmosphere. Which substance exhibits these traits?  
 (A) argon (B) chlorine (C) nitrogen (D) oxygen

Ex Output:
C


Ex Input:
Some types of bacteria can only live where oxygen is not present. These bacteria were well adapted to life on Earth over 2 billion years ago. Which of the following changes caused many of these bacteria to become extinct?  
 (A) the slow movement of tectonic plates (B) the varying temperatures of each season (C) an increase in volcanic activity under the oceans (D) an increase in the number of photosynthetic organisms

Ex Output:
D


Ex Input:
Which set of conditions will produce an electric current in a closed loop of wire?  
 (A) a magnet touching the loop of wire (B) a magnet at rest inside the loop of wire (C) a magnet at rest outside the loop of wire (D) a magnet passing through the loop of wire

Ex Output:

D