根据句意，用括号中所给单词的适当形式或句子的语法要求填空。
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.