21.     I need another dictionary because ________ cover is dirty and ________ page is missing.
A. a ; a                      B. a ; the                    C. the ; a            D. the ; the 
22.     This cake is very sweet. You ________ a lot of sugar in it. 
A.should put          B.could have put      C.might put  D.must have put
23.   — Professor Wang, thank you so much for giving us this wonderful speech.
— ________
A. It doesn’t matter.                                          B. That’s right.
C. Never mind.                                            D. My pleasure.