What is the purpose of the RMAN recovery catalog？（） 

A It must be used because all RMAN-related backup and recovery metadata information is contained in it.

B It provides a convenient， optional， repository of backup- and recovery-related metadata.

C It provides the ability to store RMAN scripts for global use by any database that has access to the repository.

D It provides a means of storing all RMAN backup sets physically in an Oracle database server. 

E It provides the ability to store backup records for more than a year.