You are maintaining your database in Oracle10g. You find that the number of languages that should be supported in your database has increased. The character set of your database is UTF8. You decide to migrate your database to the AL16UTF16 national character set.   How will you migrate your database from UTF8 to AL16UTF16？（）  

• A、 by using the RMAN utility
• B、 by using the export/import utility
• C、 by using the ALTER DATABASE command
• D、 by enabling the change tracking feature