17. Tom has three sisters. All of them are married.
=> Tom has three sisters, all of whom are married.
18. I recently went back to Paris. It is still as beautiful as a pearl.
=> I recently went back to Paris, which is still as beautiful as a pearl.
19. I recently went back to Paris. I was born in Paris nearly 50 years ago.
=> I recently went back to Paris, in which I was born nearly 50 years ago.
20. Do you know the music? It is being played on the radio.
=> Do you know the music which is being played on the radio?
21. You didn’t tell us the reason. We have to cut down our daily expenses for that reason.
=> You didn’t tell us the reason for which we have to cut down our daily expenses.
22. The day was rainy. She left on that day.
=> The day on which she left was rainy.
23. I’ve sent him two letters. He has received neither of them.
=> I’ve sent him two letters, neither of which he has received.
24. That man is an artist. I don’t remember the man’s name.
=> That man, whose name I don’t remember, is an artist.
25. One of the elephants had only one tusk. We saw these elephants at the zoo.
=> One of the elephants which we saw at the zoo had only one tusk.