Answer: B. Upton Sinclair
The muckraker that influenced regulation of the meatpacking industry is Upton Sinclair.
Step-by-step explanation:
Upton Sinclair is an famous American writer. He wrote over 100 books but in the book The Jungle he has mentioned about the meat packing facilities. He mentioned the ill behaviour of packing the rotten and bad meats that shocked the public.
His statement of the diseased meat packing system led to the establishment of federal food safety laws. Even a major reform movement was initiated in the United States.