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.
--------
Question: Air is composed of many different substances. Which of the following components of air is a compound rather than an element?  
 (A) Argon, Ar (B) Oxygen, O2 (C) Water, H2O (D) Nitrogen, N2

Answer: C


Question: Typically, sedimentary rocks are formed  
 (A) only in erupting volcanoes. (B) only under great pressure and high temperatures. (C) below Earth's surface as magma cools and crystallizes. (D) from materials that settle.

Answer: D


Question: NASA's Kepler Mission has collected information about main-sequence stars with characteristics similar to the Sun. What is the most common color of these stars?  
 (A) blue (B) white (C) red (D) yellow

Answer:
D