Your database is in ARCHIVELOG mode. On Friday evening， you perform an online database backup by using the BACKUP DATABASE command at the Recovery Manager （RMAN） prompt and close the  database. On Monday， the System Administrator informs you about the failure of two hard disks. One of the lost disks contains two datafiles， HR1.DBF and HR2.DBF， both of which belong to a read/write tablespace named HR. The disk also contains a datafile， USERS.DBF， which belongs to a read/write tablespace named USERS. You need to restore and recover the database backup that was performed on Friday evening. After mounting the database， you issue the following RMAN commands：        RMAN>RESTORE DATABASE；        RMAN>RECOVER DATABASE；   After successfully executing these RMAN commands， you issue the following statement using SQL*Plus：        SQL>ALTER DATABASE OPEN；   You receive the following errors when attempting to open the database：        ORA-01157： cannot identify/lock data file 10 see DBWR trace file        ORA-01110： data file 10： ’D:///USERS.DBF’   What is the cause of these errors？（）