21. —— Do you mind my opening the window? It’s a bit hot in here.  

—— __________, as a matter of fact. 

A. Come on             B. Yes, I do                  C. Yes, my pleasure      D. Go ahead

22. The biggest whale is ______ blue whale, which grows to be about 29 meters long —-- the height of _______ 9-story building.

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

23. Most Americans would prefer to keep their problems _______ themselves, and solve their problems ______ themselves.                       

A. in; on                      B. by; to                             C. for; to                     D. to; by