A cumulative (also called differential) backup always captures every change made since the last full backup, not since the previous cumulative backup. In this schedule, the full backup occurred on Sunday, so every subsequent cumulative backup, regardless of which day of the week it runs on, references that same Sunday full as its baseline and grows in size as the week progresses, since it must include the accumulating set of changes since that fixed reference point. By Thursday, the cumulative backup therefore contains all changes made across Monday, Tuesday, Wednesday, and Thursday relative to Sunday's full backup state, which is correctly described as 'all data that has changed since Sunday.' Option A is incorrect because a cumulative backup does not re-capture unchanged data already present in the full backup, only the deltas. Option C incorrectly anchors the comparison to Monday, which would describe an incremental backup chain reset point, not how cumulative backups are defined. Option D similarly misplaces the reference point. Restoring from a cumulative scheme only ever requires the last full plus the single most recent cumulative backup, which is the operational advantage of this approach over incremental chains.

Reference topic: Data Backup and Deduplication - Full, Incremental, and Cumulative (Differential) Backup Methods.