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: As the molecules of water begin to slow down they go into a phase where they are no longer able to easily move past each other. The water is passing through a phase change and will     
 (A) remain a mixture. (B) remain a compound. (C) become an element. (D) become a compound.

A: B
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Q: When gasoline in a car engine is burned, only about 15 percent of the gasoline is converted into mechanical energy. This is because most of the energy in the gasoline is  
 (A) transformed into heat. (B) stored for use at a later time. (C) changed into chemical energy. (D) used to make the vehicle move.

A: A
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Q: The Sun is classified as a star. Which characteristic identifies the Sun as a star?  
 (A) The Sun spins on its axis. (B) The Sun is located outside the Milky Way galaxy. (C) The Sun is part of the Big Dipper. (D) The Sun produces light and energy in a nuclear reaction.

A:
D
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