Jacob riis, Upton Sinclair, Lincoln stiffens, and Tarbell are all associated with what american literary moment?

Died January 6, 1944. Bridgeport, Connecticut. American journalists. "I aimed at the public's heart, and by accident, I hit it in the stomach." - Upton Sinclair, on the public reaction to his 1906 novel The Jungle. Jacob Riis, Upton Sinclair, Lincoln Steffens, and Ida Tarbell were the best-known of the so-called muckrakers