— You ought to have learnt all these sentences by heart.  

— ____, but I forgot everything when I was asked to recite them in front of so many students.   [ ]

A. So I ought to

B. So I did

C. So must I

D. So did I

构成肺门阴影最主要的结构是（）

A.肺动、静脉

B.神经

C.主支气管

D.肺组织

E.淋巴结