Which Statement Is True Regarding Differential / Incremental Backups

Multiple Choice

Which statement is true regarding differential / incremental backups?

A) A differential backup copies all files changed since the last full or differential backup.
B) An incremental backup copies all files changed since the last full backup; doesn't mark files as backed up.
C) Differential backups copy all files to the selected media and marks files as backed up.
D) Incremental backups copy all files changed since the last full or incremental backup and marks files as backed up.