The poor living conditions of the working class in industrial cities, is the right answer.
During the first half of the twentieth century or the Progressive era, Lincoln Joseph Steffens was one of the muckrakers. He authored the "McClure's, called Tweed Days in St. Louis", a series of articles. These articles were later compiled in a volume named The Shame of the Cities. His work focused on the poor living conditions of the working class in industrial cities.
