在下列定语从句中，填入适当的介词。

1. The pencil ______ which he wrote was broken.

2. He built a telescope ______ which he could study the skies.

3. The woman, ______ whom I learned the news, is a nurse.

4. The wolf ______ which the sheep was killed was shot.

5. She has three children, all ______ whom are at school.

6. There is a tall tree outside, ______ which stands our teacher.

7. My glasses, ______ which I was like a blind man, fell to the ground and broke.

8. In the dark street, there wasn't a person ______ whom she could turn for help.

9. The age ______ which children can go to school is seven.

10. His bike ______ which he went to work was stolen last night.

11. Do you know the building ______ which is flying a red flag?

12. Ours is a beautiful school, ______ which we are proud.

13. The desk ______ which Jack is leaning is John's.

14. He bought a book yesterday, the author ______ which is a teacher.