1. c

2. d

3. c

4. a

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1. b

2. d

3. d

4. a

5. b

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1. The girl who is sitting by Jack is Mary.

2. Can you understand the question which he asked you last time?

3. Is that the girl who (whom) we saw on TV last night?

4. Jack London, who wrote "Iron heel", is a famous American writer.

5. Hanoi, which is the capital of Vietnam, hosted 22nd Sea Games.

6. The bed on which I sleep has no mattress.

7. The girl to whom Peter is talking is Mary.

8. The woman at whom I was looking smiled.

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1. electricity

2. alternative

3. non-renewable

4. participants

5. cultural