A Differential backup process:

A.
Backs up data labeled with archive bit 1 and leaves the data labeled as archive bit 1

B.
Backs up data labeled with archive bit 1 and changes the data label to archive bit 0

C.
Backs up data labeled with archive bit 0 and leaves the data labeled as archive bit 0

D.
Backs up data labeled with archive bit 0 and changes the data label to archive bit 1

Explanation:
Archive bit 1 = On (the archive bit is set).
Archive bit 0 = Off (the archive bit is NOT set).
A full backup backs up all files regardless of whether the archive bit is 1 or 0 and sets the archive bit to 0.
When the archive bit is set to ON, it indicates a file that has changed and needs to be backed up. Differential
backups back up all files that have changed since the last full backup – all files that have their archive bit value
set to 1. Differential backups do not change the archive bit value when they backup a file; they leave the archive
bit value set to 1.Incorrect Answers:
B: Backs up data labeled with archive bit 1 and changes the data label to archive bit 0. – This is the behavior of
an incremental backup, not a differential backup.
C: Backs up data labeled with archive bit 0 and leaves the data labeled as archive bit 0. – If the archive bit is set
to 0 (Off), it will only be backed up with a Full backup. Differential and incremental backups will not back up the
file.
D: Backs up data labeled with archive bit 0 and changes the data label to archive bit 1. – If the archive bit is set
to 0 (Off), it will only be backed up with a Full backup. Differential and incremental backups will not back up the
file.

https://en.wikipedia.org/wiki/Archive_bit