Answer: B. Department
Step-by-step explanation:
The key unit in a filing segment represents the main element or keyword that is used to organize and retrieve information. In the filing segment "Fire Department City of Seattle," the key unit is "Department."
The term "Department" is the most specific and essential part of the segment that indicates the primary subject or entity being referenced. In this case, it refers to the specific department, which is the "Fire Department."
The other elements in the segment, "City of Seattle," provide additional context and clarification about the location or jurisdiction of the Fire Department. However, when it comes to organizing and retrieving information, the primary focus is on the "Department" aspect, which is the core subject of the segment.