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: Which question will best help a student determine the composition of an unknown substance?  
 (A) Is the sample warm or cold? (B) How valuable is the sample? (C) Has the sample ever been melted? (D) Does the sample conduct electricity?

A: D
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Q: Tanya investigates which household objects are attracted to magnets. Which will help her make a conclusion?  
 (A) a prediction (B) a hypothesis (C) a list of supplies (D) a table of results

A: D
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Q: Several species of fish live in a classroom aquarium. Students notice that the gills of one type of fish move faster than the gills of the other fish. Which of these statements is the best hypothesis on this observation?  
 (A) Fish have a two-chambered heart. (B) Some fish are much larger than others. (C) Fish need different amounts of oxygen. (D) There are six types of fish in the aquarium.

A:
C
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