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.