Who were the Pinkertons?

The correct answer is C private detectives hired by the mill’s manager.

The Pinkertons, officially known as the Pinkerton National Detective Agency, were a private security and detective agency founded in the United States in the 19th century. They were often hired by businesses and large corporations to investigate crimes, protect assets, and break up labor disputes. They became well-known for their involvement in various labor conflicts, often working against striking workers and unions.