$\text{Answer :}$

3. the daughter/Mr Hill 

$\text{Mr Hill's daughter}$

4. the name/ this street

$\text{The name of this street}$

5. the gardens/ our neighbors 

$\text{Our neighbors' garden}$

6. the children/ Don and Mary 

$\text{ Don and Mary's children}$

7. the wedding/ the friend/ Helen 

$\text{Helen's friend's wedding}$

8. the ground floor/ the building

$\text{The ground floor of the building}$

9. the car/ the parents/ Mike 

$\text{Mike's parents' car}$

10. the economic policy/ the government

$\text{The econimic policy of the government}$

11. the money/ the gangsters

$\text{The gangsters' money}$

12. the tail/ the horse

$\text{The horse's tail}$

13. the house/ the people we met in Spain

$\text{The house of the people we met in Spain.}$

14. the arm/ the chair 

$\text{The arm of the chair}$

15. the monthly meeting/ the club 

$\text{ The monthly meeting of the club}$

16. the work/ last year

$\text{The work of last year}$

17. the death/ someone important

$\text{The death of someone important}$

18. the middle/ the night

$\text{The middle of the night}$

19. the room/ my sisters 

$\text{My sisters' room}$

20. the door/ the garage

$\text{The door of the garage.}$

$\text{Good luck !}$

3, Mr Hill's daughter

4, The name of this street

5, Our neighbors' garden

6, Don and Mary's children

7, Helen's friend's wedding

8, The ground floor of the building

9, Mike's parents' car

10, The econimic policy of the government

11, The gangsters' money

12, The horse's tail

13, The house of the people we met in Spain.

14, The arm of the chair

15, The monthly meeting of the club

16, The work of last year

17, The death of someone important

18, The middle of the night

19, My sisters' room

20, The door of the garage.