题干
-- Is that your sweater?
-- .
A：No, it's
B：Yes, it is
C：Yes, it isn't
答案(点此获取答案解析）
B
-- Is that your sweater?
-- .
A：No, it's
B：Yes, it is
C：Yes, it isn't
、
满足
，那么向量
与向量
的夹角为