(Two words separated by an oblique, e.g. the/a, indicate that either is a possible answer. The first word is normally the preferred answer.)

1. a, the; a, a
2. an, the, the
3. a, the, -, -
4. the, a, the, -, -, (the)
5. a, -, the, a
6. a, a/the, an, the
7. a,-, an, the, the, the, the
8. a, the, the
9. a, a
10. the, the, the, the, an
11. -. -. (the), a
12. a, the, the
13. the, a, the, the, the
14. -; -, -, -
15. The, the, the; the, the
16. the, the, a, -: (the), the, the, -
17. a
18. a; the; a: a
19. a, the: a, -; The, the
20. -, the; the; a, an