1. b: 1 percent, or even less.

Many civilizations referred to as "seafaring civilizations" throughout history certainly had no more than a tiny percentage of their population traveling at sea. And no one, to the best of my knowledge, built a permanent society out in the middle of the ocean.*

2. Not sure what the question means, but in the context of the first question, and at present, I'd say e: country. It wouldn't take much progress to make it b.

3. 1 percent of the population of the U.S. would be 3 million people. I think the U.S. could be considered "spacefaring" with a thousand people in space. Many people would say that having a permanently occupied space station fills the bill.

*Anthropologists? Why is this? Why has no one ever built a floating society? Probably no shortage of places to live on land.