1. I wasn't at home last night. I was **at** the theatre.
2. She is standing **at** the back of the line.
3. We are going to visit my relatives **in** Da Nang next month.
4. Look at the structures **on** the screen.
5. My son is **at** school now. He's taking part in summer camp.
6. The plane landed safely **at** Noi Bai international airport.
7. Our office is **on** the 5th floor.
8. The Prime Minister always lives **at** No.10 Downing Street.
9. My son sat **in** the back seat of the taxi.
10. You are welcome to come with us **in** our car.
11. Everyone, please open your book **to** page 72.
12. When he was **at** university, he was an excellent student.
13. Somebody is standing **at** the door and knocking.
14. Peter's house is **at** the end of the street.
15. There were too many people **on** the bus.