题干
--- I hear Robert has gone to Harvard University for his master’s degree.
--- Oh, how nice! Do you know when he ____?
--- Oh, how nice! Do you know when he ____?
A：was leaving
B：left
C：had left
D：has left
答案(点此获取答案解析）
B
底面BCD，若
，则侧棱AB与底面BCD所成的角为（ ）