An empowered agile team showed impressive progress in the first four iterations, but now the product owner has noticed low output in the latest five iterations without any apparent reason. What could be the cause of this situation? 

Technical debt has set in and the team's output will keep dropping until the cause is eliminated. 

The team worked on low-complexity stories from the backlog in the first four iterations. 

There is most likely a specific under-performing team member slowing the team down. 

The team was in the storming stage of the development and now have moved to norming.