Ответ:
1. We couldn’t have the picnic because it was raining.
Версия 2
It was raining so we couldn't have the picnic
2. They lost the game because they played badly.
Версия 2
They played badly so they lost the game
3. I couldn’t visit my parents because I was at the conference.
Версия 2
I was at the conference so I couldn't visit my parents
П.С. Сделано две версии так как не указано в каком порядке ставить предложения