Here are the combined sentences:

1. The book was too expensive, so I wanted to buy it.
2. He married a girl called Jill, whom he met there.
3. The boy just laughed when his dog bit me.
4. My brother Jack, who plays the piano very beautifully, has just come back from Australia.
5. The student, who is very poor, gets the scholarship.
6. My teacher punished the student who was naughty.
7. They didn’t study their lesson, so they had bad marks.
8. She ate a peach, which was still green.
9. Although the sun was shining, the water was cold.