— How many students are there in the classroom?

— _____ I don't know where they have gone. [ ]

A. No one.

B. None.

C. Nobody.

D. Nothing.

奥-弗（Austin-Flint）氏杂音的发生最可能与以下那种因素有关（）

A.血流加速

B.肺动脉高压

C.左房巨大血栓

D.主动脉瓣狭窄

E.主动脉瓣关闭不全