17.  He has been studying…

18.  We have been working…

19.  It has been raining…

20.  He has been donating…

21. The government has beentrying…

22. I have been volunteering…

23.  …, don`t they?

24.  …, did she?

25.  …, hasn`t she?

26.  …, aren`t they?

27. …, can it?