偶氮染料进入小肠上皮细胞的方式（）

A.简单扩散

B.易化扩散

C.主动转运

D.过滤

E.吞噬

I know Mr Brown； we ＿＿＿＿＿＿ to each other at an international conference.

A．are introduced

B．have been introduced

C．were introduced

D．had been introduced