How does data deduplication work?

A.
It references files that have been previously stored and only backs up files that have changed
since they were last backed up.

B.
It references blocks of data that have been previously stored and only stores new backup data
that is unique.

C.
It identifies rarely-accessed data on SSD and migrates it to HDD.

D.
It automatically moves data between RAID levels to conserve disk space.