题干
--- ________ I remind you of is to return the book to our English teacher.
---I will give it to him _________ I see him.
---I will give it to him _________ I see him.
A：That; immediately
B：What; the moment
C：What; while
D：Whether; once
答案(点此获取答案解析）
B
作一直线与椭圆 
相交于A、B两点，若 
点恰好为弦 
的中点，则