"a" or "an"

Fill in the blanks.
1. He is honest boy.
2. That is useful book.
3. That is old house.
4. That is small ant.
5. orange is sweet.
6. That is heavy school bag.
7. I want glass of water.
8. That is girl.
9. We have old grandmother.
10. I am nurse.
11. That is ugly picture.
12. This is car.
13. It is doll.
14. I have friend.
15. It is Barbie doll.