题目

一广告气球被一束平行光线投射到水平面上,其投影为椭圆,离心率是,则这束光线对于水平平面的入射角为A.60°                                                              B.30°C.45°                                                              D. arctan若平面α,β的法向量分别为u=(2,-3,5),v=(-3,1,-4),则（    ）A.α∥β                                       B.α⊥βC.α,β相交但不垂直                            D.以上均不正确