Apple Certified Support Professional (ACSP) Practice Exam

Time Machine operates on a differential backup system, meaning it efficiently tracks and saves only the modifications made to files and the items that have changed since the last backup. This approach significantly reduces the amount of data that needs to be transferred and stored, allowing for faster backups and minimizing the use of disk space.

When a backup is initiated, Time Machine evaluates the files in the active file system and identifies which files have been altered. Instead of duplicating entire files or the entire file system each time, it only updates the portions of files that have been modified. This functionality is a key advantage of Time Machine, as it allows users to maintain a comprehensive and up-to-date backup of their files without the overhead that would come from backing up unchanged files repeatedly.

The other options, such as copying every changed file or asking for user permission to back up changes, don't align with Time Machine's design and efficiency goals. Time Machine’s primary focus is on automating the backup process while keeping resource use low and backup times short. This makes option C the accurate description of how Time Machine functions with changed files during the backup process.