Plurals - the odd ones out!

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Across
  1. 3. woman
  2. 5. person
  3. 6. deer
  4. 8. aircraft
  5. 10. mouse
  6. 12. trout
  7. 15. plural of roof
  8. 16. plural of loaf
  9. 17. plural of hankerchief
  10. 19. fish
  11. 20. plural of book
  12. 22. plural of calf
  13. 23. plural of cliff
  14. 24. foot
Down
  1. 1. moose
  2. 2. sheep
  3. 4. men
  4. 5. plural of potato
  5. 7. plural of echo
  6. 9. child
  7. 11. plural of valley
  8. 13. tooth
  9. 14. plural of toy
  10. 18. species
  11. 21. goose