Answer B is correct. The FORMAT clause of the BACKUP command initializes a tape and places a new header on the tape. The remaining options do not enforce these actions.
For more information, see the following sources:
Chapter 6, "Database Maintenance"
SQL Server 2005 Books Online: "SQL Server Database Engine, Administering the Database Engine, Backing Up and Restoring Databases, Managing Backups, Using Backup Media"
Within MSDN Library, go to MSDN Home, MSDN Library, Servers and Enterprise Development, SQL Server, SQL Server 2005, Backing Up and Restoring Databases, Managing Backups, Using Backup Media, Initializing Backup Media.