Here are the sentences converted into passive voice:

1) Many rubber plantations can be found on the map of our country.
2) Things made of rubber have been seen by me.
3) Her decaying tooth was shown by Susan.
4) I am told by my parents to practice my music lessons.
5) These pieces of furniture need to be painted.
6) The food is put in the refrigerator at home by people.
7) Good marks are always gotten by him at school.
8) Their teeth and mouths must be kept clean by them.
9) Nam was told by our form teacher to put the tools back in the workshop.
10) An English speaking club will be opened by my school.

If you need help with the second part related to joining sentences, let me know!