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 Q]: 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
[EX A]: C

[EX Q]: Rocks that contain fragments of bones, shells, and plant remains are most likely  
 (A) crystals. (B) igneous. (C) sedimentary. (D) metamorphic.
[EX A]: C

[EX Q]: What would happen if a magnet was placed in the center of a plastic bowl containing a mixture of iron filings and sand?  
 (A) The sand will be repelled by the magnet. (B) The iron filings will be attracted to the magnet. (C) The sand will be attracted to the magnet. (D) The iron filings will be repelled by the magnet.
[EX A]:
B