题干
--I wonder if you could spare a little time to help with my English tonight?
--_____. I have no extra work to do anyhow.
A：Sure, go head
B：No, well done
C：No, indeed
D：Certainly, after you
答案(点此获取答案解析）
A
，半径为1，
且
，则向量
在
方向上
的投影为
