21. Many parents think that it is ______waste of time to chat on ______Internet all day .
A. a; the B. the; 不填 C. a; a D. the; the
22. The two pupils , of the lecture , started to talk in a very low voice .
A. tiring ; boring B．tired ; boring
C. tired ; bored D．tiring ; bored
23. Who do you think is for the cruel conflict ?
A. blamed B．blaming C．to be blamed D．to blame
