Образуйте множественное число существительных
1. burglary 2. key 3.knife 4. knowledge 5. air 6. army 7.formula
8.child 9.wife 10.bottle 11.guitar 12.cloth 13.mouse 14.tooth
15.tomato 16.video 17.sheep 18.fruit 19.plan 20.tie 21. house
22.glass 23.fruit 24.path25.cigarette 26.bed27.cat 28.snow 29.holiday
30.cheese 31/vertebra 32. boy 33.child

1. burglary - burglaries2. key - keys3. knife - knives 4. knowledge - uncountable  5. air - uncountable (but if we talk about smb's manners, the plural form ("airs") is used; the sense, however, is absolutely different) 6. army - armies 7. formula - formulas / formulae 8. child - children9. wife - wives 10. bottle - bottles11. guitar - guitars 12. cloth - cloths (not to be confused with "clothes"!)13. mouse - mice 14. tooth - teeth15. tomato - tomatoes 16.video - videos 17. sheep - sheep18. fruit - fruits (when we talk about the successful results of our work; the plural form is also used in specialised literature) or uncountable (more often) 19. plan - plans 20. tie - ties 21. house - houses22. glass - glasses or uncountable (if we talk about the substance) 23. fruit - see above (№18)24. path - paths25. cigarette - cigarettes 26. bed - beds (countable, if we don't take some fixed expressions into account)27. cat - cats 28. snow - uncountable in most cases; I don't want to burden your memory with too many details, I don't think it necessary to explain when it can be countable :) 29. holiday - holidays 30. cheese - uncountable or countable ("cheeses") (when we talk about different types of this food) 31. vertebra - vertebrae 32. boy - boys 33. child - children