Which of the following is a sign that food in a fast-food restaurant must be discarded?

The correct choice indicates that food must be discarded when it has reached its expiration date. This is because expiration dates are established to ensure food safety and quality. Consuming food past this date poses a risk to health, as it may no longer be safe to eat. Fast-food restaurants must adhere strictly to expiration dates to comply with health regulations and maintain customer safety.

In a fast-food environment, maintaining the highest standards of food safety is essential. While it's important for food to smell good and be served at an appropriate temperature, these factors alone do not guarantee the food's safety if it has already expired. Similarly, food that is sold within four hours still needs to be safe to consume, but reaching the expiration date is a definitive indicator that it should be discarded to prevent any potential health issues from arising.