Of the choices, the best, and correct answer for the cost increase is technical debt. Technical debt is the backlog of things that should be done, but aren’t, because of a push to deliver features, such as maintenance, regular cleanup,
and refactoring. This increases development costs in future iterations because these tasks will need to be done at some point in time. It’s easier and more proficient to factor in the time needed to complete this maintenance during
the iteration, instead of doing it at some other time. The other responses are incorrect because the hours worked are mapped against each user story; scope creep refers to the small, undocumented changes that enter the project; in
the question, there’s no proof that additional testers have been added to the project team.