Past Perfect, Past Perfect Continuous or Past Simple?

1. I had worked/had been working for the company for three months before I realised my neighbour also worked there.
2. As soon as George had finished the race, he drank 3 glasses of water.
3. Everything was white because it had snowed/had been snowing all night.
4. My parents were really happy when I qualified because they had always wanted me to be a doctor.
5. She was exhausted when she got out of the pool because she had swum 3 kilometers.
6. We had only sat down when the waitress came to take our order.
7. I could tell from their faces that they had argued/had been arguing about something.
8. Our dinner wasn’t ready because I had forgotten to switch the oven on.
9. By the time the doctor arrived, the baby had been born.
10. After John had finished his dinner he went straight to bed.