backup and recovery difficulties

i m new here. I have finished three papers of OCP DBA 8i.
I am currently studyin for Backup and Recovery
Please help me with some difficulties

I will be glad if some one could help me with the answers here.

1.Your database is configured in ARCHIVELOG mode. Which three types of backups can be performed? (Choose three)

A.**Open database backups.
B.**Operating system backups when the database is closed.
C.Online control file backups using the ALTER CONTROLFILE BACKUP command.
D.Online tablespace backups using the ALTER DATABASE BACKUP TABLESPACE command.
E.**Online control file backups using the ALTER DATABASE BACKUP CONTROLFILE command.

2.Work is done by Recovery Manager through ____?

A.**PL/SQL packages.
B.External procedures.
C.Operating system scripts.
D.Operating system commands.

3.Which statement regarding Recovery Manager with a database operating in NOARCHIVELOG mode is true?

A.Recover manager requires a recovery catalog.
B.**Recovery Manager supports multi-level incremental backups.
C.Recovery Manager is compatible with enterprise backup utility.
D.Recovery Manager only works in conjunction with a tape subsystem.

4.Which technique does Oracle use to perform full backups of data files?

A.The server process reads and backs up the entire file.
B.*The server process reads the entire file and skips blocks that have never been used.
C.The server process reads the entire file and skips blocks assigned its temporary segments.
D.The server process reads the entire file and skips blocks that currently are not being used.
E.The server process reads the entire file and skips blocks that are unchanged from the last backup

5.Which statement about an open database backup is NOT true?

A.The database must be available in ARCHIVLOG mode.
B.The database is available for use during backups.
C.*All the database files copied are consistent to a point-in-time.
D.An operating system backup of the database files is required.