Answer C is correct. Single-user startup uses the m switch. The minimal configuration startup (-f) starts an instance of SQL Server with minimal configuration. The option is useful if the setting of a configuration value (for example, overcommitting memory) has prevented the server from starting. The option enables the sp_configure allow updates option. By default, allow updates is disabled.
For more information, see the following sources:
Chapter 1, "Installing and Configuring SQL Server 2005"
SQL Server 2005 Books Online: "SQL Server Database Engine, Administration How-to Topics, Managing Services How-to Topics, Managing SQL Server from the Command Prompt Using sqlservr.exe, How to: Start an Instance of SQL Server (sqlservr.exe)"
"Using Startup Options," http://msdn.microsoft.com/library/default.asp?url=/library/en-us/adminsql/ad_1_start_8m43.asp
Within MSDN Library, go to MSDN Home, MSDN Library, Servers and Enterprise Development, SQL Server, SQL Server 2000, Starting, Pausing, and Stopping SQL Server, Starting SQL Server, Using Startup Options.