How do historians learn about people who live in the earliest historical eras?

37. what was hitler's "final solution"? a) the construction of walled ghettos in polish cities to hold "undesirable" groups b) a plan to exterminate all jews living in regions controlled by the third reich c) a series of fake medical experiments on jews conducted on topics such as oxygen deprivation d) a plan to force all "undesirable" groups to become "useful members" of the third reich