first part: A nation-state is a state that has one centralized government (making it a sovereign state), the majority share the same culture, and their political boundaries and cultural boundaries line up with each other.
(It gets more in-depth political wise but that's the basic idea of it)
second part: Korea is technically not a nation-state today because it is two separate states. North Korea is actually considered more of a cult than a nation-state because of the isolation and sanctions set in place.
not sure if that is the answer you were looking for, if you want me to explain it more in-depth or differently let me know :) hope this helps
Personally I would say it's A (apart from the installation costs which may make it a little expensive) but it does involve certain aspects of D also as wind energy doesn't cause pollution. So either A or D!
