Write a or an: 1. ... a pencil sharpener 2. ... ruler 3. ... rubber 4. ... pencil case 5. ... notebook 6. ... atlas 7. ... blackboard 8. ... book 9. ... school bag 10. ... pen 11. ... pencil 12. ... notepad 13. ... timetable

1. a pencil sharpener
2. a ruler
3. a rubber
4. a pencil case
5. a notebook
6. an atlas
7. a blackboard
8. a book
9. a school bag
10. a pen
11. a pencil
12. a notepad
13. a timetable

Правило: перед согласным звуком употребляется a, перед гласным звуком — an.