Final answer:
The thermometer should be located in the warmest part of the cold storage unit to ensure the entire unit does not exceed the maximum desired temperature.
Step-by-step explanation:
The location of the thermometer in a cold storage unit is crucial to ensure its reliability and the safety of the stored items, especially in a food storage context. The best option is B. In the warmest part of the unit. This is because ensuring the warmest part of the unit is at the desired temperature guarantees that the rest of the unit is at least as cold as, if not colder than, the set limit. You do not want to position the thermometer near the door (option A) since frequent opening can cause temperature fluctuations. Placing it in the coldest part (option C) could give a misleading indication that foods are properly stored when they may not be if they are located in a warmer part of the unit. Attaching it to the ceiling (option D) is also ineffective because cold air sinks and the temperature at the ceiling can differ from the air where the stored goods are located.