Hello!
The answer is: C. 40°F to 140°F
Why?
According to the Food Safety and Inspection Service (which belongs to the United States Department of Agriculture) keeping food at room temperature for too long, will increase the possibility of bacteria creation such as Campylobacter, Salmonella Enteritidis, Escherichia coli, and Staphylococcus aureus.
Temperatures above 40°F thru 140°F creates a favorable environment for bacteria proliferation, it's called the danger zone for foods. The recommendations are wether keep the food hot (above 140°F) or keep the food cold (below 40°F).
Have a nice day!