1. His chair
= a boy's chair

2. Her ruler
= a girl's ruler

3. This book
= a book close to me

4. Their table
= Two pupils' table

5. A pencil-case
= Any pencil-case

6. A window
= Any window

7. Her notebook
= A girl's notebook

8. This door
= The door close to me

9. His head
= A boy's head

10. Her pencil-case
= A girl's pencil-case

11. This light
= The light close to me

12. That book
= a book far from me

13. His pencil-case
= A boy's pencil-case

14. A notebook
= Any notebook

15. That door
= The door far from me

16. His notebook
= A boy's notebook

17. his chair
her ruler
this book
their table
a pencil-case
a window
her notebook
this door
your red pen
his head
her pencil-case
this light
that book
his pencil-case
a notebook
that door
his notebook

18. etc.