Final answer:
Muckrakers of the Progressive Era supported several causes, including the creation of federal safety standards in industrial workplaces. Their work led to significant legislative reforms aimed at addressing the social inequities of their time. Therefore the correct answer is D the creation of federal safety standards in industrial workplaces.
Step-by-step explanation:
The issues supported by the Progressive Era muckrakers included several societal challenges, but the option that directly aligns with their causes is: D the creation of federal safety standards in industrial workplaces. The muckrakers exposed harsh realities such as child labor, unsafe working conditions, and the need for regulation of trusts and monopolies. These investigative journalists were pivotal in initiating reforms that would eventually lead to legislative changes like the Meat Inspection Act and the Pure Food and Drug Act. By highlighting these social inequities, they encouraged everyday Americans to demand reforms that would foster a more equitable and just society.