How does the modern era differ from the post-classical era? a. economies are based on agriculture during the modern era, but were based on manufacturing during the post-classical era. b. the modern era has seen the rise of powerful imperial states, while the post-classical era was characterized by smaller city-states. c. the modern era is characterized by global exchange of ideas and goods, while this kind of exchange was mostly regional during the post-classical era. d. nations rely on raw materials from within their own borders during the modern era, but they relied on materials from abroad during the post-classical era.