2. That's the box where we keep the books.
That's the box in which we keep the books.
That's the box we keep the books in.
3. The girl to whom John was talking is my sister.
The girl John was talking to is my sister.
The girl who/that John was talking to is my sister.
4. The house where I spent my childhood was demolished.
The house in which I spent my childhood was demolished.
The house I spent my childhood in was demolished.
5. That's the man to whom we spoke on the day of the murder.
That's the man we spoke to on the day of the murder.
That's the man who we spoke to on the day of the murder.
6. The friend I was travelling with spoke German.
The friend with whom I was travelling spoke German.
The friend who I was travelling with spoke German.
