You are maintaining the SALES database of a company. You have never backed up the USERS tablespace that is currently offline. On Sunday， you issued the following commands：   CONFIGURE DEFAULT DEVICE TYPE TO sbt；   CONFIGURE BACKUP OPTIMIZATION ON；   CONFIGURE RETENTION POLICY TO REDUNDANCY 3；   From Monday to Saturday， you performed the following actions：   Day                         Action  Monday                BACKUP DATABASE  Tuesday                BACKUP DATABASE  Wednesday              BACKUP DATABASE  Thursday               BACKUP DATABASE  Friday                 BACKUP DATABASE  Saturday               BACKUP DATABASE  How many times will the backup of the USERS tablespace be performed？（）

• A、 The backup will not be performed at all.
• B、 three times
• C、 four times
• D、 six times