题目

已知点，是抛物线：上的两点，且线段过抛物线的焦点，若的中点到轴的距离为2，则（ ）A. 2 B. 4 C. 6 D. 8 答案：【答案】C【解析】利用抛物线的抛物线的定义写出弦长公式，利用中点横坐标来求得弦长.设，，则，而的中点的横坐标为，所以.故选C.听对话，回答1-3题。1. What time does Alice get up? A. 6:00. B. 6:30. C. 6:45. 2. What does Mike have for breakfast? A. Apple juice and cakes. B. Tea and bread. C. Cakes and eggs. 3. What foods does Alice like best? A. Bread and milk. B. Cakes and eggs. C. Fish and hamburgers.