Final answer:
Cooked TCS food must be cooled to 70°F (21°C) within 2 hours to ensure safety by preventing the rapid growth of bacteria.
Step-by-step explanation:
The question you've asked relates to the proper cooling procedures for cooked time/temperature control for safety (TCS) food. To ensure safety and prevent the rapid multiplication of bacteria, TCS food must be cooled down to 70°F (21°C) within 2 hours of cooking. It is crucial to cool foods rapidly to prevent foodborne illness because bacteria multiply most rapidly between 40°F (4°C) and 140°F (60°C), a range known as the 'danger zone'. Thus, the correct answer to your question is a) 70°F (21°C).