21. A. any                    B. other                       C. the                        D. a

　　22. A. for example        B. on average               C. in fact                   D. by chance

　　23. A. with                   B. on                           C. in                         D. of

　　24. A. that                    B. those                       C. which                    D. what

　　25. A. because              B. although                  C. in case                   D. so that

　　26. A. weak                  B. lost                          C. normal                  D. keen

　　27. A. mental                B. physical                   C. biological              D. psychological

　　28. A. territory             B. land                         C. surroundings          D. area

　　29. A. supply of            B. call for                    C. cost of                   D. desire for

　　30. A. balanced             B. restricted                  C. destroyed               D. increased