A.1 000个              B.1 250个                C.900个                D.800个

A.                  B.                    C.                  D.

A.4                    B.-4                     C.10                    D.-10

A.a=,b=                                   B.a=,b=-

C.a=-,b=                                   D.a=-,b=-

①若l⊥α,l∥β,则α⊥β;

②若α⊥β,α∩β=l,m⊥l,则m⊥β;

③若lβ且m和l不互相垂直，则m和β不互相垂直；

④若α⊥β,l∥α，则l⊥β.

其中正确的命题是

A.②③                 B.②④                 C.①③                 D.③④

A.(8,1)               B.(-8,4)               C.(-4,2)               D.(-8,-1)

A.2                  B.4                  C.6                  D.8

A.                  B.                  C.                 D.

A.{1,3,4,5,6}            B.{1,3,5}                C.{4,6}                D.{3}