Final answer:
A refrigerator should be maintained at or below 4 degrees C (40 degrees F) to prevent bacterial growth, with the optimal answer being option c. It is recommended to use a built-in or separate thermometer to monitor this.
Step-by-step explanation:
The temperature to maintain a refrigerator is at or below 4 degrees C (40 degrees F). This temperature range is crucial for inhibiting bacterial growth in refrigerated foods and ensuring food safety. It's essential to monitor the temperature with a thermometer, especially during a power outage. If the temperature remains below 40 degrees F when the power is restored, the food is safe. However, if it exceeds 40 degrees F for more than two hours, the food may be unsafe to eat.