1. arrived - was watching
2. was preparing - rang
3. were you doing - arrived
4. learned - was working
5. were you sitting - began
6. visited - was touring
7. fell - was crossing
8. did you see - were waiting
9. driving - broke
10. met - was walking
Cấu trúc: một hành động đang diễn ra thì bị một hành động khác làm gián đoạn thường có ''when'' thì hành động đang diễn ra dùng thì quá khứ tiếp diễn, hành động xen vào dùng thì quá khứ đơn.