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:
You wish to closely observe a small insect. Which tool is the best to use?  
 (A) a balance (B) a test tube (C) a telescope (D) a magnifying glass

Ex Output:
D


Ex Input:
Which organ is the site of gas exchange between the body and the environment?  
 (A) spleen (B) liver (C) lungs (D) pancreas

Ex Output:
C


Ex Input:
Which device would most likely be used to produce light energy?  
 (A) a laser (B) a radio (C) a toaster (D) a microwave

Ex Output:

A