Let me answer this question. I just became a high school math teacher. . Ha ha. . This question is simple. I can see that you are a beginner. I don't count, so I know the answer is A. Introduce two methods. First, if the second equation is divided by k twice at the same time, a new standard elliptic equation will be obtained. Remember that the standard elliptic equation with 1 on the right can be used to calculate A, B, C and E. You may be familiar with the standard elliptic equation format, but the long axis A and short axis B of this second equation have obvious changes, so the focal length C you calculate must change. Because these values are all changing, you can choose A. If you don't believe me, you can also use a 1, b 1, a2 and b2 of the standard equation to calculate C 1 and C2 of two ellipses respectively, and then calculate e 1 and e2, which must be equal. . . Students, study hard. High school math is very interesting. . . .