Which of the following foods must be refrigerated to prevent bacteria growth?

The requirement to refrigerate foods is essential for safety, particularly for products of animal origin. Foods such as meat, poultry, fish, eggs, and dairy products are prone to harboring harmful bacteria like Salmonella, Listeria, and E. coli. When these foods are left at room temperature for extended periods, bacteria can multiply rapidly, leading to foodborne illnesses.

Refrigeration slows down the growth of these bacteria, making it a crucial step in food safety for items that come from animals. This includes raw and cooked meats, seafood, and any dairy products. Therefore, the correct answer emphasizes the importance of refrigeration specifically for these types of foods to maintain their safety and quality.

The other options do not carry the same level of risk or do not need refrigeration to the same extent. Foods in unopened sealed containers might be shelf-stable depending on their type, hard-boiled eggs with intact shells can often be stored safely at room temperature for a short period, and cotton candy generally does not provide an environment conducive to bacterial growth. Thus, identifying animal-origin foods as needing refrigeration is a fundamental principle of food safety management.