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.