Dear student,

The answers to your question is :-
In first blank it is - natural gas
In the second blank it is - coal
And in the third blank it is - petroleum

So, now, the complete answer of the first line is - FOSSIL FUELS ARE NATURAL GAS, COAL and PETROLEUM .

And, the Process of separation of different constituents from petroleum is calledREFINING .

I hope that you got your answer.

Good luck!