c#中如何获取listbox中选中值的问题

StringBuilder ConponPerson = new StringBuilder();
            for (int i = 0; i < lb_tzs.Items.Count; i++)
            {
                if (lb_tzs.Items[i].Selected == true)
                {
                    ConponPerson.Append(lb_tzs.Items[i].Value);

//ConponPerson.Append(lb_tzs.Items[i].Text);
                    ConponPerson.Append(",");
                }

            }
Response.Write("选中的项的value:" + ConponPerson);

//Response.Write("选中的项的Text:" + ConponPerson);