A.平行于π
B.在π上
C.垂直于π
D.与π斜交
[判断题]A.对B.错
[单选题]A.B.C.D.
[单选题]A.4B.2C.1D.0.5
[单选题]A.12B.14C.18D.20
[单选题]A.条件(1)充分,但条件(2)不充分B.条件(2)充分,但条件(1)不充分C.条件(1)和条件(2)单独都不充分,但条件(1)和条件(2)联合起来充