1.已知全集U=R,集合A={x | 1<x≤3},B={x | x>2},则A∩CUB等于
A.{x | 1<x≤2}                                            B.{x | 1≤x<2}   
C.{x | 1≤x≤2}                                            D.{x | 1≤x≤3}
2.已知角α的终边经过点P(m,-3),且cosα=- ,则m等于
A.-              B.               C.-4                          D.4
3.已知向量a=(1,2),a·b=5,| a-b |= ,则| b |等于
A.                        B.                       C.5                            D.25
4.设Sn为等差数列{ an }的前n项和,若S8=30,S4=7,则a4的值等于
A.                          B.                           C.                         D. 、
5.已知直线m、l和平面α、β,则α⊥β的充分条件是