5.B what

6.B -> have worked

7.C -> buying

8.B -> to

9.A -> is

10.A had taken

11.B competition

12.B pollution

13.A alternative

15.C collector

16.D extinction

17.B spaceman

18.C going

19.A guests

20.D Silver Anniversary

21.B post office

22.C spacecraft

23.C which

24.A that

25.C extinct

26.B non-renewable

27.A fossil fuel

28.C If I hadn't stayed up late last night, I wouldn't have been tired

29.B It was football that he played the whole afternoon

30.A If you had told me the story, I could have helped you

31.B He apologized for having to leave early

14, C

15, A

16, C

17, B

18, C

19, A

20, D

21, B

22, C

23, C

24, D

25, C

26, B

27, A

28, C

29, B

30, A

31, B

1, B

2, D

3, C

4, A

5, what --> that

6, worked --> have worked

7, to buy --> buying

8, for --> to

9, are --> is

10, A

11, B

12, D

13, A