21. Ketty’s birthday party was ____ success. We sang and danced until it came to ___ end at ten.    

A. a ; the     B a ; an     

 C ; an     D the ; the

22. An opinion is ____ someone believes is true but has not been proved.

A.  that      B. which   

C. what      D. how

23. Miludeer, a species with large horns, which used to be ____ in China long ago, is a rare animal nowadays.

A. ordinary    B. common  

C. popular    D.  usual