NDA English Rearranging Sentences in a Paragraph

S1: The machines that drive modem civilization derive their power from coal and oil.
S6: Nuclear energy may also be effectively used in this respect.
P : But they are not inexhaustible.
Q : These sources may not be exhausted very soon.
R : A time may come when some other sources have to be tapped and utilised.
S : Power may, of course, be obtained in future from forests, water, wind and withered vegetables.
The proper sequence should be