11. After David had gone home, we arrived.
12. Before we took a look around the shops, we had had lunch.
13. When we got out of the office, the flight had gone out.
14. By the time we started our work, she had explain everything clearly.
15. Before my mother came home, my father had watered all the plants in the garden.
16. Bill sad it was the fisrt time he eaten sushi.
17. Lan said that she had broken her glasses the day before.
18. If I didn't work at night, I had attended the evening classes.