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.