President Roosevelt's first reaction to Upton Sinclair's The Jungle is best described as O outrage toward the meat-packing industry.
disgust and anger toward meat-packing industry workers.
surprise at the public's demand for healthy livestock.
disbelief and distrust of Sinclair's claims.

Option: disbelief and distrust of Sinclair's claims

Explanation:

The Jungle by Upton Sinclair pointed out the violations of the meatpacking production. The people reacted in loathing after reading this book. President Theodore Roosevelt placed an urgent investigation into the meat industry. Upton Sinclair had gone undercover for weeks inside various Chicago meatpacking industries to examine for his book. The book focuses on Packingtown and its poor sanitation and hygiene. By keeping mind and for the benefits of people in America, Congress passed acts including the Pure Food and Drug Act of 1906 and Meat Inspection Act after getting signed from President.