=>

B/

1. They could not help you because they were not here.
They were not here so they could not help you.
2. I can't go out because it's raining.
It's raining so I can't go out.
3. We haven't got any food so we are going shopping.
We are going shopping because we haven't got any food.
4. There was fog so their flight was delayed.
Their flight was delayed because there was fog.
5. The film was boring so we decided to go home.
We decided to go home because the film was boring.
6. I couldn't do this exercise so I asked Tom for help.
I asked Tom for help because I couldn't do this exercise.

C/

1. The holidays were so cheap that they booked one immediately.

6. They had such a good time on a farm that they didn't want to come back home.

7. Mr.Smith is such a strong man that he can lift up a heavy box easily.

8. It was such a warm evening that we had dinner outside in the garden.
9. It was such a lovely evening that my grandmother wanted to have a walk in the park.
10. It is such a large stadium that it can hold 60000 people.