17. liz bought many souvenirs in Ho Chi Minh City .
(-)Liz didn't buy many souvenirs in Ho Chi Minh City.
(?) Did liz buy many souvenirs in Ho Chi Minh City?
18. I was very tired after the trip.
(-)I wasn't very tired after the trip.
(?)Were you very tired after the trip?
19.they are watching my father's new motorbike.
(-)They aren't watching my father's new motorbike.
(?)Are they watching your father's new motorbike?