$\text{Answer :}$
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
$\text{The door of the garage.}$
$\text{Good luck !}$