A.1条       B.2条        C.3条         D.4条

A.1条                                        B.2条

C.3条                                        D.4条

A.1条                   B.2条                  C.3条                   D.4条

已知平面α与β所成的二面角为80°，P为α、β外一定点，过点P的一条直线与α、β所成的角都是30°，则这样的直线有且仅有

1. A.
   1条
2. B.
   2条
3. C.
   3条
4. D.
   4条