Ответ:

20. already

21. yet

22. never

23 already

24. before

25. My sister has been to Spain twice.

26. Mike and Garry have gone to London for the day.

27. I have never been to America before.

28. Mum has gone shopping. She’ll be back this afternoon.

29. Mr. Smith is tired. He has gone to the airport and back twice this morning.

30. Has your teacher been to England? 

31. They have never ridden on a rollercoaster.

32. My best friend has never been to Italy.

33. Have you ever explored a haunted mansion?

34. Has he ever visited The Great Wall of China?

35. I have never flown in a helicopter.