1. We are living in an age ____ many things are done on computer.
2. We are living in an age ____ we have a lot of things to learn about.
3. I can think of many cases ____ students obviously knew a lot of English
    words and expressions but couldn't write a good essay.
4. I can think of many cases ____ you know nothing about.
5. I want to know the date ____ you were born.
6. I have remembered the date ____ I forgot just now.
7. Do you know the reason ____ he is absent today?
8. That is the reason ____ I want to know.
9. This is the factory ____ his father works.
10. This is the factory ____ his father built.
11. The key ____ she was opening the door broke.
12. The library ____ we often go on Sundays is not far from our school.
13. No one knows the reason ____ she is leaving so early.
14. At last they came to a river ____ a new bridge is being built.
15. The old man always wears his glasses ____ he can't see anything.