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 time