1. Brenda is a friend. I went on holiday with her.
=>Brenda, whom I went on holiday with is a friend
2. This is Mr. Smith. His son Bill plays in our team.
=>This is Mr. Smith, whose son Bill plays in our team.
3. Her book was published last year. It became a best-seller.
=>Her book, which became a best-seller was published last year.
4. This is the bank. We borrowed the money from it.
=>This is the bank, where We borrowed the money from
5. I told you about a person. She is at the door.
=>I told you about a person, who is at the door.