Present at the meeting                  ．

A．Mr. Liu was, who taught us English

B．was Mr. Liu, who taught us English

C．was who taught us English, Mr. Liu

D．Mr. Liu, who taught us English, was

社会分工的发展是公共关系产生的（）。

A.客观基础

B.本质特征

C.核心

D.重要保障