The key answer of exercise 3

a)

1. She's bought a new pair of trousers.
2. I haven't brought my credit card.
3. Have Anna and Kay been / gone shopping?
4. Has your sister ever worked as a model?
5. I've been to the shopping centre twice today.
6. We haven’t sold anything on eBay recently.

b)

1. Have you ever had; had; did you buy; bought
2. Have you ever been; have; went; did you stay; found
3. Have you ever bought; you've never worn; have; did you buy; bought
4. Have you ever lost; have; did you lose; left
5. Have you ever done; haven't; tried; met

c)

1. Dan's bought something on eBay.
2. Dan's booked a flight online.
3. Dan's never stayed in an Airbnb house or flat.
4. Jon and Mia haven't bought something on eBay.
5. Jon and Mia have never booked a flight online.
6. John and Mia have stayed in an Airbnb house or flat.

d)

1. Have you ever bought something on eBay?
2. Have you ever booked a flight online?
3. Have you ever stayed in an Airbnb house or flat?