exercise 2 Check the meaning if needed.
1. nephews
2. nieces
3. churches
4. dishes
5. bays
6. hobbies
7. factories
8. alleys
9. opportunities
10. scenarios
11. mosquitoes/mosquitos
12. tomatoes
13. lives
14. thieves
15. roofs
16. geese
17. men
18. trout
19. headquarters
20. crises

exercise 3 Write the singular forms of the following nouns. Remember to include the article a or an as well.
1. a switch
2. a berry
3. a half
4. a knife
5. a mouse
6. a child
7. an echo
8. a series
9. a phenomenon
10. a person
11. a leaf 
12. a reindeer
13. a Japanese person