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: Which difference between water and ice results in ice floating on cold water?  
 (A) heat (B) shape (C) density (D) volume

A: C
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Q: What type of force keeps the planets orbiting the Sun?  
 (A) gravitational (B) magnetic (C) electrical (D) nuclear

A: A
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Q: What determines if twins are identical?  
 (A) their genes (B) their behavior (C) their environment (D) their personalities

A:
A
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