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.