A.0
B.1
C.-π/2
D.π/2
[单选题]A.0B.1C.-π/2D.π/2
[单选题]A.0B.1C.-1D.2
[单选题]A.垂直B.斜交C.平行不重合D.重合
[单选题]A.B.C.D.
[单选题]A.-2B.-1C.0D.2