According to the PMBOKĀ® Guide (specifically within the Plan Human Resource Management process), the Staffing Management Plan is a formal component of the Human Resource Plan (and by extension, the overall Project Management Plan).
The Relationship: The Human Resource Plan provides guidance on how project human resources should be defined, staffed, managed, and eventually released. The Staffing Management Plan is the specific section within it that handles the " timetable " and " mechanics " of the staff.
Contents of the Staffing Management Plan:
Staff acquisition: Where the people come from (internal vs. external).
Resource histograms: A tool for showing the number of hours a person or department will be needed over time.
Staff release plan: How and when team members will leave the project.
Training needs: Any skills the team lacks that must be acquired.
Recognition and rewards: How the team will be motivated.
Compliance and Safety: Regulations the project must follow.
Modern Note: In the current PMBOKĀ® Guide (6th and 7th editions), this is now integrated into the Resource Management Plan, which covers both human and physical resources. However, in the context of this question set, it remains a subsidiary of the Human Resource Plan.
Analysis of Other Options:
A. organizational process assets: OPAs are external to the project plan; they are the templates, historical files, and procedures already existing in the company. While you use a template from the OPAs to write your plan, the plan itself is a project document, not an OPA.
B. resource calendar: This is actually the other way around. The Staffing Management Plan includes or informs the resource calendars by defining when resources are needed. The plan is the high-level management document; the calendar is the specific data of availability.
D. Develop Project Team process: This is a process (an action), not a document. The Staffing Management Plan is an input to this process, but it is not " part of " the process itself. Processes are verbs; plans are nouns.