Any combination of unique letters, numbers, or blanks, which describes and identifies any activity or...

An Activity ID is a unique combination of letters, numbers, or blanks that describes and identifies any activity or task shown on a project schedule. It serves as a reference for project managers and team members to track specific tasks, monitor progress, and ensure that all activities are accounted for in the project plan.

Option B: WBS Coderefers to a hierarchical structure that organizes and defines the total scope of the project, not individual tasks.

Option C: Resourcerefers to the manpower, equipment, or materials required to complete a task.

Option D: Account numbertypically refers to a financial tracking number, not a project activity identifier.

Therefore,A. Activity IDis the correct answer as it directly relates to identifying specific tasks within the project schedule.