根据对话内容的理解，选择正确答案。
(Some classmates are talking about their weekend.)
Linda: I stayed at home and studied over the weekend. I studied for my English test on Saturday. Yesterday I wrote a geography paper. In the evening I talked to my pen pal (笔友) on the phone. What did you do?
Tim: I had a good time. On Saturday morning I played tennis, in the afternoon I went to the beach, and in the evening I went to Nancy's birthday party. On Sunday I went to the mountains with my friends.
Mary: Oh, your weekend was great. But mine was boring. I stayed at home the whole (全)weekend. I cleaned my room and washed my clothes. I even watered the flowers. And only in the evening I watched TV for a short time. Did you go out, Dave?
Dave: No, I didn't. I stayed at home and watched TV on Saturday. Yesterday I watched a movie on TV, Fearless. It was very exciting.
”是“方程
表示焦点在y轴上的椭圆”的 （ ）