Final answer:
A single entrance door is not a unique element of Multi-Dwelling Units (MDUs) compared to Single Family Dwellings (SFDs) for service calls, while shared demarcation points, multiple access points, and building layout considerations are unique to MDUs.
Step-by-step explanation:
The element that is NOT a unique feature of a Multi-Dwelling Unit (MDU) as opposed to a Single Family Dwelling (SFD) during a service call is d) Single entrance door. MDUs, such as apartment buildings or condos, often have multiple units that share common infrastructure. Consequently, they have characteristics like a) a shared demarcation point, where the service provider's responsibilities end and the in-building wiring begins, b) multiple access points for maintenance and service purposes, and c) building layout considerations which affect the distribution of services throughout the complex. In contrast, SFDs typically have one main entrance that serves a single family or household, not a distinguishing feature for service calls in MDUs.