Final answer:
The urban population in the United States grew more quickly before the Civil War, while the rural population increased at a slower rate.
Step-by-step explanation:
According to the line graph, the urban population in the United States grew more quickly before the Civil War. This can be observed from the data points on the graph, where the urban population goes from 1 in 1800 to 13 in 1880. After the Civil War, the urban population continued to grow, but at a slower rate compared to before.
The rural population, on the other hand, increased at a slower rate compared to the urban population. This can be seen from the data points on the graph, where the rural population goes from 5 in 1800 to 35 in 1880, and then to 50 in 1920.
Therefore, the correct answer is d. The urban population grew more quickly before the Civil War.