The correct answer is: B. incremental backup
A full backup is a backup of all data on a computer system. An incremental backup is a backup of only the files that have changed since the last full or incremental backup. A differential backup is a backup of only the files that have changed since the last full backup.
Incremental backups are the most space-efficient type of backup because they only back up the files that have changed since the last backup. This can save a lot of space, especially if you are backing up large files or folders that do not change often.
Full backups are the least space-efficient type of backup because they back up all of the data on a computer system. This can be a waste of space if you are only backing up a few files or folders.
Differential backups are more space-efficient than full backups, but less space-efficient than incremental backups. This is because they back up all of the files that have changed since the last full backup, but not the files that have changed since the last incremental backup.
In conclusion, incremental backups are the most space-efficient type of backup.