Помогите пожалуйста выбрать правильный вариант.
12.Mary ___ her seatbelt when the accident happened that’w why she was badly hurt.
1.didn’t wear
2.wasn’t wearing
3.hadn’t worn
4.hadn’t been wearing

13.When I was young I ___ that people over 40 were old. Now that I am 40 myself I don’t think so.
1.thought
2.was thinking
3.used to think
4.had thought

14.She wasn’t interested in the book as she ___ it.
1.wasn’t understanding
2.hadn’t understood
3.didn’t understand
4.couldn’t understand