A. Time Machine identifies the 1MB of file changes, copies those changes to a new file on the backup drive, and keeps both the new backup file and the original backup file.

B. Time Machine identifies the 1MB of file changes, copies those changes to a new file on the backup drive, creates a 500K parity file, and keeps all three files: the two new files representing the 1MB of file changes and the original backup file.

C. Time Machine copies the 6MB file to the backup drive and keeps both the new backup file and the original backup file on the backup drive.

D. Time Machine copies the 6MB file to the backup drive and deletes the original backup copy of the file from the backup drive.