21．In recent years ____ global warming is becoming ____ concern for people all over the world.

A．the; the      B．/ ; /     C．/ ; a       D．the ; /

22.—What made you so unhappy?

—             .

A.My mother was ill          

B.That my mother was ill 

C.Because my mother was ill  

D.Because of my mother being ill

23.—Sara has just come back from New York and she looks very happy.

—She ________ her trip very much.

A. might enjoy     

B. should have enjoyed

C. might have enjoyed    

D. must enjoy