Concept:Sequencing sentences in a paragraph based on logical flow.
Explanation:The passage starts with S1 introducing two Nobel laureates and ends with S6 relating to India.
Sentence P follows S1 because "their" refers to the two winners mentioned in S1.
Next, sentence R explains that productive activity has spillovers.
Sentence Q then defines the term "externality" for those spillovers.
Finally, sentence S states that both winners studied externalities, linking back to P.
Thus, the correct order after S1 is P, R, Q, S.
Option B (PRQS) matches this sequence.
Answer:Option B (P R Q S)