题干
— Were you surprised by the ending of the film?
—No, I _______ the book, so I already knew the story.
A：was reading
B：had read
C：am reading
D：have read
答案(点此获取答案解析）
B
在曲线 
上，点 
，当点 
中点 
的轨迹方程．
，则
等于( )