如何检查用户是否具有SQL Server 2008 R2中的系统管理员权限

I have a application that should only allow access to users who are system admins on the db. What sql script or query can I execute from the c# code that, given a username, can determine if he/she has system admin privileges system specs: sql2008R2 db, .net 2.0, c#I have a application that should only allow acc