4. Insert 'a', 'an', or nothing (–).

1. nothing 2. a man 3. a bank 4. nothing 5. nothing 6. a cashier 7. a piece 8. of paper 9. nothing 10. a robbery 11. a gun 12. nothing 13. a paper 14. nothing 15. a message 16. nothing 17. a cashier 18. nothing 19. a paper 20. a paper bag 21. an paper bag 22. nothing 23. nothing 24. the robber 25. nothing