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: What happens when water flows over a rock for a long period of time?  
 (A) erosion (B) flooding (C) breakage (D) evaporation

A: A
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Q: What happens to the water vapor in an air mass as it ascends?  
 (A) It freezes. (B) It condenses. (C) It vaporizes. (D) It polarizes.

A: B
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Q: Which of these shows how frozen water changes as the temperature of the air increases?  
 (A) Gas -> liquid -> solid (B) Solid -> gas -> liquid (C) Liquid -> gas -> solid (D) Solid -> liquid -> gas

A:
D
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