1. was repairing, arrived
2. was eating, rang
3. was riding, dropped
4. saw, were driving
5. was watching, broke down
6. were talking, came
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Принцип: сложное предложение - 2 части. 1 часть - продолжительное действие, 2 часть - резкое действие. Например: Я мыл посуду, когда мама пришла. - I was washing up when my mother came home.