Viết lại câu sao cho nghĩa không đổi

6. Air is made up of many gases which We breathe

7. Jackie Chan is famous actor whose sister I know well

8. The house needs mending which we are living in it

9. This tree should be cut down which The branches are dead

10. Tell me the reason which You left the city for

11. That river is not safe for swimming whose water is polluted