TASK DEFINITION: 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.
PROBLEM: Greenhouse gases in the atmosphere absorb infrared radiation from Earth's surface and re-radiates some of it back to Earth. Which of these gases have the most significant impact on the temperature of Earth's atmosphere?  
 (A) nitrogen and argon (B) oxygen and sulfur dioxide (C) carbon dioxide and water vapor (D) hydrochloric acid and hydrogen

SOLUTION: C

PROBLEM: Which of these is a structure that is present in all organisms?  
 (A) a tissue (B) a cell (C) a stomach (D) a brain

SOLUTION: B

PROBLEM: Which color of light is produced when all of the colors of visible light in the electromagnetic spectrum are combined?  
 (A) gray (B) white (C) black (D) brown

SOLUTION:
B