The key answer of exercise 13

a)

1. when
2. while / when
3. when
4. while / when
5. while / when
6. when
7. when
8. while / when

b)

1. I was getting dressed when Guy phoned and said he was ill, so I decided to go by train.
2. Unfortunately, while / when I was talking to Guy on the phone, the cat walked over my shirt, so I had to iron another one.
3. While / When I was walking to the station it started snowing and I got cold.
4. The train was delayed because it started snowing and when it finally arrived I was frozen!
5. I fell asleep while / when I was sitting on the train and missed the station.
6. I got off at the next station and decided to walk to Kyra's house. When I reached the end of the road I realised I was lost.
7. I didn't have my mobile so I looked for a phone box to call a taxi.
8. When I arrived at Kyra's house it was nearly midnight and people were going home!