维生素C缺乏所致鼻出血的机制是（）。

A.神经末梢退行性变而导致黏膜萎缩

B.黏膜发生剧烈充血、血运停滞

C.鼻黏膜上皮及其腺体逐渐出现退行性变

D.鼻黏膜的血管壁通透性和脆性增加

E.鼻黏膜上皮组织干燥、过度角化

Before he finally sent its copies off to be handed out among members of the committee, he went over it again and made sure that no item of importance was ______.

A．checked out

B．crossed out

C．dropped out

D．left out