Forms :: Retrieving Value Through Combo Box Based On Query

I have 4 tables:

table 1: two fields: t_code (primary key), town_name
table 2: two fields: Distri_code (Primary Key), Distri_name
Table 3:two fields: T_D (Primary key), t_code (foreign key), distri_code (foreign key)
Table 4:A_T (Prim key), T_D (Foreign key), area_code (foreign key)
table 5: area_code (pri key), area

I want to make a form on table 4 where both foreign keys are numbers. On the data entry form on this child table, i am trying to link towns and areas. At the front end form, i want a combo or list item showing town_name (table1) and distri_name (table 2).

Once the end user selects the required town and district from available options, i want to retrieve T_D from table 3 through query based on input from both values and save it table 4 in place of T_D along with area_code, which i can retrieve simply from table 5.