Value of Second dropdownlist disappears

I have two dropdownlist. On Selection of City(first) dropdownlist. I get the values of Area(second) dropdownlist.
But after saving when I came again to check the value, the value of second dropdownlist gets disappears. I dont know why this happens.
Here is my code below:-
[WebMethod] public static string GetState(string City) { string State = ""; DataTable DtState = new DataTable(); OracleConnection Conn = new OracleConnection(System.Configuration.ConfigurationManager.ConnectionStrings["OracleConn"].ToString()); Conn.Open(); OracleDataAdapter ObjPriState = new OracleDataAdapter("select state_code||'~'||Country_Code State_Country from XXCUS.XXACL_PN_STATE_V where state_code = (select state_code from XXCUS.XXACL_PN_CITY_V where city_code='" + City + "')", Conn); ObjPriState.Fill(DtState); if (DtState.Rows.Count > 0 ...