A. No, cities, while popular for some odd reason, are just a system designed to help live your life, however shorter it is in the pollution. Cities can fall under the category of wanting a Mercedes when you have a Seering; you don't need it, but its a want and it might help you a little more in small ways.
B. There is no real Social Equality. People try to make it so, but there are alot of cases (and I mean alot) where it doesn't happen. Civilization still runs though. And dictatorships are still civilizations.
C. I could build a village with rocks or wood, and it would still be a civilization. A civilization is not defined by 'Skyscrapers' but by people itself. I wouldn't judge a book being very good if I just glanced at its cover. I would judge it only by reading it.
D. I would have to say, of all your choices, this comes the closest. But its not necessarily true. A system of trade creates better conditions of life and it helps cement groups of people, but a true civilization comes from the people themselves.
