A.45°       B.60°     C.90°     D.不确定

A.45°                    B.60°                    C.90°                    D.不确定

A.45°                B.60°                  C.90°                 D.120°

过抛物线焦点F的直线与抛物线相交于A、B两点,若A、B在准线上的射影分别是A₁、B₁,则∠A₁FB₁等于(    )

A.45°                B.60°                  C.90°                 D.120°