Which of the following conditions must exist prior to restoring a system database in SQL Server 2012?

Which of the following conditions must exist prior to restoring a system database in SQL Server 2012?
A. The hard drive must be reformatted.
B. You must detach the user databases from the SQL 2012 instance.
C. The SQL Server 2012 instance must be started in single-user mode.
D. The SQL Server 2012 instance must be removed.