Two data files have been deleted at the operating system level by accident. Your database is running in ARCHIVELOG mode and online backups are taken nightly. One of the data files that has been deleted belongs to the USERS tablespace on the other belongs to the SYSTEM tablespace. How can you recover from this situation？（）

• A、Shut down the database, restore the two data files and then start up the database. 
• B、Take the system and users tablespace offline, restore the two data files, recover the two datafiles, and then bring the SYSTEM and USERS tablespaces online. 
• C、Shut down the database, restore the two data files, start up the database in MOUNT mode, recover the two data files, and then alter the database open. 
• D、Take the SYSTEM and USERS tablespaces offline, recover the two datafiles and then bring the SYSTEM and USERS tablespaces online.