Concept:The correct sequence of the jumbled sentences is determined by logical flow and continuity of ideas.
Explanation:S1 introduces social networking as grouping individuals.
P logically extends S1 by noting that social networking is most popular online, setting the stage for online discussion.
Q naturally follows P, stating that for online social networking, websites are commonly used.
R then names these websites as social sites, clarifying the subject.
S explains that social networking websites function as an online community of Internet users, which directly leads into S6 about community members sharing common interests.
Thus, the proper sequence is P, Q, R, S.
Answer:PQRS