题干
I should very much like to have gone to that party of theirs, but ＿＿＿＿＿.
A：I’m not invited
B：I was not invited
C：I have not been invited
D：I had not been invited
答案(点此获取答案解析）
B
，则向量a与b的夹角等于（ ）
