During the early twentieth century, the action taken to address the issues shown in the diagram of working conditions during the Second Industrial Revolution was labor reformers securing better working conditions through legislation.
The working conditions during the Second Industrial Revolution were often harsh, with long hours, low wages, and unsafe working conditions.
Labor reformers sought to improve these conditions by advocating for better wages, shorter working hours, and safer working conditions.
They also pushed for the passage of labor laws that would protect workers' rights and improve their working conditions.
Therefore, option C is the correct answer.