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.

[Q]: 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
[A]: C


[Q]: Which two protein molecules are essential for muscle contraction and relaxation?  
 (A) actin and myosin (B) collagen and tubulin (C) hemoglobin and myoglobin (D) amylase and polymerase
[A]: A


[Q]: Which is the correct order of the planets from the Sun?  
 (A) Mercury, Venus, Earth, Saturn, Uranus, Jupiter, Mars, Neptune (B) Mercury, Earth, Mars, Venus, Saturn, Jupiter, Neptune, Uranus (C) Mercury, Venus, Mars, Earth, Jupiter, Uranus, Saturn, Neptune (D) Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
[A]:
D