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: Two forms of boron are naturally occurring, boron-10 and boron-11. What difference exists between a boron atom with a 10 atomic mass units (amu) and a boron atom with 11 atomic mass units (amu)?  
 (A) amount of neutrons (B) number of electrons (C) size of protons and neutrons (D) size of electrons and electron cloud

A: A
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Q: Which tool would be best to use to determine how long it takes a cup of water to boil?  
 (A) balance (B) hot plate (C) stopwatch (D) thermometer

A: C
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Q: What is the most common element found in the compounds that make up ocean water?  
 (A) nitrogen (B) oxygen (C) carbon (D) silicon

A:
B
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