Asp.net dropdownlist code

public static DropDownList dropDown(string col1,string col2,string tblName,DropDownList ddl)
   {
       SqlConnection con = Database.GetConnection();
       SqlCommand cmd = new SqlCommand("select "+col1.Trim()+","+col2.Trim()+" from " + tblName.Trim() + "", con);
       SqlDataAdapter da = new SqlDataAdapter(cmd);
       DataSet ds = new DataSet();
       da.Fill(ds, tblName);
       ddl.DataSource = ds;
       ddl.DataTextField = col1;
       ddl.DataValueField = col2;
       ddl.DataBind();
       return ddl;
   }