Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

Q: Although they differ vastly in hardness, pencil lead and diamonds both contain carbon.

A: Although they differ vastly in hardness, pencil lead and diamonds both contain what element?
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Q: Oil is the most commonly used source of energy in the world.

A: What is the most commonly used source of energy in the world?
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Q: Conduction is the transfer of thermal energy between particles of matter that are touching called.

A:
What is the transfer of thermal energy between particles of matter that are touching called?
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