What tools can you use to understand words you do not know? how can you tell what sources are good and what sources are not?

Which choice is a major detail from paragraph two? a) the great wall is a large network of several walls and towers. b) the great wall looks like a long wall snaking its way across china. c) the great wall was constructed over hundreds of years beginning in 221 b.c. d) the great wall construction encouraged several independent kingdoms to unite.