1. S1:The machines that drive modern civilization derive their power from coal and oil S6:Nuclear energy may laso be effectively used for this purpose 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 utilized. S:Power,of course,may be ontained in the future from forests,water,wind and withered vegetables The correct sequence is