A.>0                             B.<0                                    C.=0                                    D. 不能确定

27. (         )

A.-                            B.                                    C.2                               D.-2

28. (         )

A.sint²                           B.cosx²                                C.2xcosx²                    D.sinx²

29. 广义积分 (        )

A.-2                              B.2                               C.0                               D. 发散

30. 下列广义积分中发散的是 (         )

A.                 B.                C.                 D.