The discovery of what led to a large population growth in the mid 1800s?

What does the country say concerning the status of free blacks living in the united states? a) they have the same rights as any other "free" people, and are full citizens. b) they have the same rights as any other "free" people, but are not properly citizens. c) they are citizens, but don't have the full rights granted to other citizens. d) they are not citizens, and have no right to petition the court.