Which influential book did Upton Sinclair write that exposed the meatpacking industry?

Upton Sinclair wrote "The Jungle," a novel published in 1906 that had a significant impact on public awareness of the conditions in the meatpacking industry. Sinclair's vivid descriptions of the harsh realities faced by immigrant workers, combined with the unsanitary practices in meat production, shocked readers and stirred public outrage. This response ultimately led to reforms in food safety practices and the establishment of regulatory frameworks such as the Meat Inspection Act and the Pure Food and Drug Act.

The other options do not pertain to the meatpacking industry: "The Grapes of Wrath" by John Steinbeck addresses the struggles of Dust Bowl migrant families during the Great Depression; "The Great Gatsby" by F. Scott Fitzgerald explores themes of wealth, class, and the American Dream in the 1920s; and "Invisible Man" by Ralph Ellison deals with African American identity in mid-20th century America. Each of these works is significant in its own right, but they do not cover the specific issues highlighted in "The Jungle."