As business increased, and the city grew with rapid strides, the necessities of the poor became the opportunity of their wealthier neighbors, and the stamp was set upon the old houses, suddenly become valuable, which the best thought and effort of a later age have vainly struggled to efface. Their "large rooms were partitioned into several smaller ones, without regard to light or ventilation, the rate of rent being lower in proportion to space or height from the street; and they soon became filled from cellar to garret with a class of tenantry living from hand to mouth, loose in morals, improvident in habits, degraded, and squalid as beggary itself." It was thus the dark bedroom, prolific of untold depravities, came into the world. -Jacob A. Riis, How the Other Half Lives, 1890

Which development most likely contributed to the conditions described by Riis?

A. The Homestead Act encouraged people to start farms in the West, and new immigrants fleeing hardship craved their own land.

B. Urban factory workers demanded immigration restrictions to protect their jobs from new immigrants willing to work for lower wages.

C. Railroads connected cities and markets from coast to coast, making it easier for new immigrants to migrate between shifting employment opportunities.

D. Mechanization shifted urban employment to largely unskilled labor, and new immigrants provided a ready pool of low-wage workers.​