부정관사 a의 쓰임 구분 부탁드려요

아래 문장에서 a가 어떤 의미로 쓰였는지 구분 부탁드려요.
1. Rome was not built in a day.
2. He eats five meals a day.
3. This is an interesting book.
4. The fox is a cunning animal.
5. There are seven days in a week.
6. She keeps a diary three times a week.