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.

Example Input: A light year is used to measure  
 (A) time. (B) distance. (C) luminosity. (D) temperature.
Example Output: B

Example 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
Example Output: C

Example Input: Geotropism is a response by plants to which force?  
 (A) gravity (B) friction (C) air pressure (D) Earth's magnetism
Example Output:
A