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: When oxygen combines with hydrogen, which substance is formed?  
 (A) water (B) vinegar (C) hydrochloric acid (D) hydrogen dioxide

A: A
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Q: One important use of coal is to produce energy for homes. Coal can be burned and converted to  
 (A) wind energy. (B) nuclear energy. (C) electrical energy. (D) solar energy.

A: C
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Q: An important rule for students to know when heating a test tube is to  
 (A) place a cork in the mouth of the test tube. (B) point the mouth of the test tube away from others. (C) hold the test tube loosely with the fingertips. (D) shake the test tube forcefully to keep contents mixed.

A:
B
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