Adifferential backup covers what data on a system?
a.
it includes data that has changed since the last full backup.
b.
it includes data that has changed since the last incremental backup.
c.
it includes only data that has changed since the last backup.
d.
it includes all data every time it is performed.

Answer is option (a) It includes data that has changed since the last full backup.

Explanation:

Differential Backup is a method used in Database Management Systems (DBMS) in which it includes the data (copies of all the files) that has changed (either created or updated or altered) since the last full backup. If it is a partial backup instead of full backup, then it is not a differential backup method as many files might have changed. Option (b) is false as the backup has to be a full backup not an incremental backup. Option (c) is false as the backup has to be a full backup ( not just a backup ), Option (d) is false as only the files that are changed is stored not the whole database since a full backup.