11. Mary ate a banana a few minutes ago.
They have just eaten a banana for a few minutes 

12. He left his house a few minutes ago.
 He has just left his house for a few minutes

13. My parents send me some money every month.
 I am sent some money by my parents every month

14. The gardener waters the plants every day.
The plants are watered by the gardener everyday.

15. Peter wrote a novel.
The novel was written by Peter.

16. Jane did a lot of homework .
 A lot of homework was done by Jane

17. People built the bridge last year.
 The bridge was built last year

18. You must do this test carefully.
This test must be done carefully.

19. They grow rubber trees in tropical countries.
Rubber trees are grown in tropical countries.

20. Children should drink milk every day.
Milk should be drunk by children everyday.

11. Mary ate a banana a few minutes ago.
They have just eaten a banana for a few minutes
12. He left his house a few minutes ago.
 He has just left his house for a few minutes
13. My parents send me some money every month.
 I am sent some money by my parents every month
14. The gardener waters the plants every day.
The plants are watered by the gardener every day.
15. Peter wrote a novel.
The novel was written by Peter.
16. Jane did a lot of homework.
 A lot of homework was done by Jane.
17. People built the bridge last year.
 The bridge was built last year.
18. You must do this test carefully.
This test must to done carefully.
19. They grow rubber trees in tropical countries. => Rubber trees are grown in tropical countries.
20. Children should drink milk every day.
Milk should to drunk by the children every day.