The project team is analyzing the release burndown chart and notices that the actual burndown line is consistently above the ideal burndown line in the last two iterations. They also observe that the scope of the work in the backlog (total work in backlog) is not increased during the same timeframe. Which of the following options could be a possible cause of this delay?

A. High team morale and productivity leading to faster completion of tasks B. Insufficient work items in the backlog, resulting in lower completion rate C. Unexpected technical challenges or dependencies causing delays in task completion D. Frequent scope changes or additions impacting the planned work