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: Oxygen reacts with iron to produce rust and with hydrogen to produce water. Which statement describes both reactions?  
 (A) A different mixture is formed in each case. (B) A different solution is formed in each case. (C) Both a change of state and of elements is involved. (D) New molecules are formed but the same elements exist.

A: D
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Q: One type of animal hatches from an egg, breathes through gills when it is young, and mainly lives on land as an adult. Into which group is this animal classified?  
 (A) amphibians (B) birds (C) mammals (D) reptiles

A: A
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Q: Which statement best describes the motion of the molecules of a solid object?  
 (A) They vibrate in place within a fixed volume. (B) They move around freely within a fixed volume. (C) They vibrate in place and take the shape of a container. (D) They move around freely and take the shape of a container.

A:
A
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