【单选题】— How does the story the emperor's new clothes _____? — Once upon a time, there was a silly Emperor who loved clothing more than anything else... [ ]
【单选题】椭圆C: x 2 25 + y 2 9 =1 的焦点为F 1 ,F 2 ,有下列研究问题及结论: ①曲线 x 2 25-k + y 2 9-k = 1 (k<9) 与椭圆C的焦点相同; ②一条抛物线的焦点是椭圆C 的短轴的端点,顶点在原点,则其标准方程为x 2 =±6y; ③若点P为椭圆上一点,且满足 P F 1 ? P F 2 =0 ,则 | P F 1 + P F 2 | =8. 则以上研究结...