Final answer:
Burn-down charts track work completed over time in the scope of agile project management. They provide a visual representation of the work remaining versus time left in a sprint, and they are essential for tracking progress toward completing sprint goals.
Step-by-step explanation:
Burn-down charts are a tool used in agile software development methodologies, such as Scrum, to visualize progress. They specifically track A) Work completed over time. This is represented by a graph showing the amount of work remaining (typically in terms of user stories, tasks, or requirements) versus the time left in the sprint. As tasks are completed, the chart shows a downward trend, indicating progress towards the sprint goal. The chart helps teams to understand if they are on track to complete their work before the sprint ends. It's different from tracking the team member hours spent, which is more about the input rather than the output of the team's work. Likewise, while product and sprint backlog changes may influence the burn-down chart, these are not the primary focus of what the chart is designed to track.