You are given a science question (hard-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: When a mixture of oxygen and hydrogen is ignited in a test tube, the reaction shown occurs. Hydrogen + Oxygen -> Water + Energy What happens to the total mass of the contents of the test tube?  
 (A) The total mass increases. (B) The total mass decreases. (C) The total mass remains the same. (D) Part of the mass is changed to heat energy.

A: C
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Q: Which is the best unit to measure distances between Earth and other solar systems in the universe?  
 (A) miles (B) kilometers (C) light years (D) astronomical units

A: C
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Q: Missy and Ethan discussed examples of the types of changes in matter. In which example is a chemical change taking place?  
 (A) A piece of metal is cut in half. (B) An ice cube melts on a counter. (C) A camper roasts marshmallows over a burning fire. (D) A baker mixes together flour and sugar to make dough.

A:
C
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