Đáp án+Giải thích các bước giải:
2Jim was standing under a tree when he heard an explosion.
3The boy fell and hurt himself while he was riding a bicycle.
4The tourist lost his camera while he was walking around the city.
5The lorry was going very fast when it hit a car.
6While I was studying in my room, my roommate was having a party in an other room.
7Mary and I were having dinner when the telephone rang.
8We were sitting in a cafe when they saw us.
9We stayed home and listened to music last Sunday.
10Tom had a car accident when he was 8 so he doesn't like driving.
11I stayed up late last night because I had a lot of exercises.
12Who saved the child yesterday.
13Mary could play the piano when she was a little girl.
14It rained heavily yesterday but he visited me.
15Jane completed her homework and went to bed.
16Pablo Picasso went to a school of art when he was 13.
17Nelson mandela became the president of Africa in 1994.
18She used to be a doctor before WWI in France.
19I was quite shy and hard-working when I was at high school.
20Mary didn't go to the cinema because she was sick yesterday evening.
