18. Concl. right.

19. Concl. right.

20. Concl. right.

21. Concl. right.

22. Concl. wrong: the right one is “Some x are y.”

23. Concl. right.

24. Concl. right.

25. Concl. right.

26. Concl. right.

27. Concl. right.