What Effect Did the Establishment of an Extensive Railway System

What effect did the establishment of an extensive railway system have on the American economy?

A) It encouraged rapid urbanization, so that by 1850 the majority of Americans in the North lived in cities.
B) It made Chicago America's financial and commercial center during the nineteenth century.
C) It created an economic bubble that led to a depression beginning in 1843.
D) It created economic connections between the Northwest and the Northeast.
E) It significantly increased the costs paid by farmers to transport their goods to market.