What physical feature made up much of the northern border of the tang dynasty?

Which events are correlated but do not necessarily have a causal relationship?

Who was the leader of the black nationalists in the 1920s?

How did the completion of the transcontinental railroad change the lives of american citizens? a-it increased the wealth of all americans and enabled them to travel more. b-it made cross-country travel too expensive for ordinary americans. c-it decreased the safety of americans who moved to settle the plains. d-it shortened travel time between the east and west for all americans.