1. He was sitting on a chair. It was uncomfortable.

-> He was sitting on a chair which was uncomfortable.

2. Do you know that lady? I repaired her car.

→ Do you know that lady whose car I repaired?

3. I bought bananas this morning. I have lost them.

→ I bought bananas this morning which I have lost

4. The film is about two people. Their plane crashed in the jungle 

→ The film is about two people whose plane crashed in the jungle.

5. They are the people. I was talking about them.

→ They are the people whom I was talking about.

6. He smokes cigarettes. They are very strong.

→ He smokes cigarettes which are very strong.

7. She's the woman. She telephoned the police.

→ She's the woman who telephoned the police.

8. Let me see the pictures. You took them at Peter's wedding.

→ Let me see the pictures which you took at Peter's wedding.

9. He's the criminal. The police are looking for him.

→ He's the criminal whom the police are looking for.

10. The man was sick. He looked very pale. 

→ The man who looked very pale was sick.