20．--Do you mind my opening the window for n while?

--　 .

　　 A.No,thanks　　 B．N0．I do　　 C. Yes,please　　 D．Yes．Better not

19．--Have you read the book Oliver Twist?

--Who　 it?

　 A.writes　　 B.wrote　　 C.has written　　 D.had written