What is a graphical schedule that relates the progress of work items to a timeline?

The correct answer is the Gantt chart, as it is specifically designed to illustrate the progression of tasks or work items against a timeline. A Gantt chart visually demonstrates the start and end dates of various activities, showing how they overlap and how resources are allocated over a certain period. It allows project managers and stakeholders to quickly understand which tasks are scheduled to occur at any given time, making it easier to track progress and identify potential delays.

In comparison, while a bar graph or bar chart schedule can display data in a visual format, it does not specifically represent the interconnectedness of time and tasks in the same way that a Gantt chart does. A bar chart is better for comparing quantities across different categories rather than illustrating project timelines.

Network diagrams are typically used to represent the relationships between tasks and to show the flow of activities in a project, but they do not provide a clear representation of the timeline for completion. A flow chart, on the other hand, is used to indicate a process or sequence of operations but does not relate activities to a specific timeline.

Thus, the Gantt chart stands out as the most appropriate graphical representation for the progress of work items against a timeline in project management.