Final answer:
The files were lost because the desktop folder was not synchronized with OneDrive.
Step-by-step explanation:
The reason Nazreen's files were lost could be due to option d., which states that the desktop folder was not synchronized with OneDrive. If she was saving her files on the desktop and they were not backed up or synced with a cloud storage service like OneDrive, then they could have been lost when her laptop was corrupted. It is important to regularly back up files and ensure they are synchronized with a cloud storage service to prevent data loss.