This book by Upton Sinclair exposed the health condition in the meat packing plants.

The Jungle (1906)

Explanation:

Sinclair´s novel was a compilation of the serial publication he wrote throughout 1905. The fictional story of an immigrant family, based on real-life stories Sinclair obtained by going undercover inside several meatpacking plants in Chicago, was aimed to expose their horrible working conditions. The book not only became one of the most famous muckraking novels, but it also created such a public outrage that led to the enactment of the Pure Food and Drug Act in 1906 aimed to better the conditions in slaughterhouses.

b or c im pretty sure