1.watched
2. were seeing -were building
3.bought
4.were reading-heard
5. were sleeping- broke
6.flew
7.opened-entered-broke
8.happened- were sleeping
9. was writing-had
10. was typing- was learning

6 they were flied to HCM city at 8pm
7 he was opened the doctor, entened the room and break something
8 the earthquake has happened while wa sleeped
9 he has wroten the textbook, when he has a headache
10she has typed the book while i learned chinese

1, was watching
2, were seeing , were building
3,bought
4, were reading / were hearing
5, slept/ was breaking
6, were flying
7, opened / entered/broke
8, happened/ was sleeping
9, were writing / had
( 5 sao nhé )