6. we had had a look around the shops, we had snack
7. worked than the light failed
had they worked than the light failed
had they worked when the light failed
8. happier than ever
9. I went to the zoo last year, I hadn't seen a real tiger before
14. they had got ready, they went out for dinner
15. Andrew found the test very easy, he had done it
16. we were watching television, a burglar broke into the house
17. After the stewardess had served lunch for passengers, she sat down