1. Mary was sick. She ate four bars of chocolate.
- Mary, who ate four bars of chocolate, was sick.
2. A woman sold me the jeans. She was a friend of my sister's.
- The woman who sold me the jeans was a friend of my sister's.
3. I've been looking for this magazine.
- This is the magazine (that) I've been looking for.
4. The flat where I lived as a child were built in 1960s.
5. The people who work in the office are very kind.
6. The dog which I found in the middle of the street is the black one.