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

[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?


[Q]: Resistors connected end to end are said to be in series.
[A]: Resistors connected end to end are said to be in what?


[Q]: Co 2 is the molecular formula of carbon dioxide.
[A]:
What is the molecular formula of carbon dioxide?