UPSC 2017 CDS I English Paper

SI: The first great discovery that man probably made was that of fire.
S6 : The animals were not clever enough to learn anything from this.
P : Fires sometimes occur by themselves in the forests perhaps by rubbing together of flints or something else.
Q : We light a fire now by a match.
R : In olden times fires were made by striking two flints against each other till a spark came for setting fire to a dry thing.
S : But matches are quite recent things.
The proper sequence should be