public static string HtmlOptionContacts(int accesslevel, int contactId, bool isAdmin)
        {
            System.Data.DataTable dt = Tab_Contact.SelectContactList(accesslevel, isAdmin ? 0 : contactId, ">=");
            //  Id, Name, Firma, Ort

            string options = string.Empty;

            for (int i = 0; i < dt.Rows.Count; i++)
            {
                //<option value="2">Option 2</option>

                int    id       = int.Parse(dt.Rows[i][0].ToString());
                string name     = dt.Rows[i][1].ToString();
                string selected = (id == contactId) ? "selected" : string.Empty;

                if (isAdmin || id == contactId)
                {
                    options += $"<option value='{id}' {selected}>{name}</option>" + Environment.NewLine;
                }
            }

            return(options);
        }