Ответ:
1) Mary was talking..., while her brother was taking a nap.
2) As she bought..., a bus drove past her.
3) I felt miserable, while my friends were laughing.
4) He was digging..., when he suddenly found...
5) In the evening they were watching TV because they had...
6) I caught.... when I was skiing...
7) She heard.... when she was listening...
8) I lost... when I was walking...
9) He called... when I was having...
10) I bought... when I was getting ready...
11) I didn't come... because I felt bad
12) The dog was sleeping whil I was watching TV
13) When the bell rang ... most of us were still writing...
14) Teacher collected... when the bell rang
15) I was writing... while you were playing...
16) Steve was driving... when he saw...
17) It was raining... when he was walking...