Final answer:
In the context of the choices provided and the nature of functional obsolescence, option d. no heating source would be the correct answer. (option d)
Step-by-step explanation:
Functional obsolescence refers to a feature of a property that is outdated and cannot be easily changed, like lacking a heating source in a home. It is unlike issues that can be fixed, such as a broken A/C unit. The concepts illustrated involve ensuring that appliances have suitable and functioning power sources. A broken A/C unit, a clogged drain, and an inoperable faucet could all potentially be repaired. However, if a house lacks a heating source, this is a more significant issue as it affects the overall functionality of the house and may not be as easily remedied without a considerable investment.
Consider if an electrical outlet is faulty, any appliance like a coffeemaker plugged into it would not work; this doesn't make the appliance obsolete -- the issue is with the power source. Similarly, if a refrigerator doesn't run as it should because of a long, inexpensive extension cord, the fault isn't with the refrigerator's functionality; it is due to an inadequate power supply that causes a voltage drop or insufficient current to reach the appliance, which compromises its performance.