The correct answer is D. Important
Step-by-step explanation:
Paragraph 5 provides information about the meaning and organization of mounds that were structures created by ancient tribes or communities. In this paragraph it is explained Mount A was for the chief of town that can be inferred was the leader or more important person in the town.
Additionally, the text explains "The closer a person lived to Mound A, the more significant he or she was in the society", in this context the word "significant" refers to the position of the person in the society in reference to the chief, and therefore this word means relevant or important as those who were important or significant in these communities lived near to the chief.