Exam PRINCE2-Practitioner topic 21 question 28 discussion

The project is now in the 'closing a project' process and the project manager is evaluating the project. The project manager has asked the team manager for the
'delivered pilot courses' to identify how many errors were found in the 'accredited classroom-based training course' during the piloting of the course. In addition, the team manager of the 'finalized materials' was asked to state how many of these errors had been fixed.
Which theme is being applied?