根据句意，用括号中所给单词的适当形式填空。
1. Playing too many computer games is ______ (harm) to you.
2. We should speak to the old man ______ (polite).
3. —How many ______ (tooth) does a dog have?
—Sorry, I have no idea. Let's search on the Internet.
4. A computer is ______ (expensive) than a TV set.
5. Have you read ______ (today) newspaper?
6. I ______ (not go) to bed until my mother came back at ten last night.
7. You need _______ (return) the comic book to the library at once.
8. My sister _______ (be) a singer since she left the school.
