A systems administrator is setting up a backup solution to follow the 3-2-1 policy. Currently, the solution is set to back up from the servers to an on-site storage server. Which of the following should the administrator configure to comply with the 3-2-1 policy?

A. Weekly full backups, with daily incremental backups
B. A second on-site storage server for backups
C. Storage snapshots
D. An off-site storage server for backups