Concept:Rearranging jumbled sentence parts by identifying the subject, its description, and the verb phrase.
Explanation:Start with the main subject: Part Q – "a group of people".
This is immediately followed by the adjective clause that describes it: Part S – "who share a common culture".
So the correct sequence begins with Q then S (QS).
Next, the remaining details "historical identity and a common descent" (Part P) come after the clause, describing what else the group shares.
Finally, the verb phrase "is called an ethnic group" (Part R) ends the sentence.
Thus the full order is QSPR.
Answer:Option A (QSPR)