Which command in DOS can be used to recover accidentally deleted files?

To recover accidentally deleted files in DOS, the correct command is UNDELETE. Here's the explanation for each option:
Option A: UNDELETE is the command used to recover accidentally deleted files in DOS.
Option B: DELETE/CANCEL is not a valid DOS command for file recovery. It seems to combine the delete and cancel concepts, which is not how file recovery operates.
Option C: RESTORE is not the correct command for recovering deleted files in DOS. It doesn't perform file recovery operations.
Option D: RECOVER is not the correct command for file recovery in DOS. It typically refers to recovering data from damaged disks, not recovering deleted files.

Therefore, Option A (UNDELETE) is the correct command to recover accidentally deleted files in DOS.