Professor Li always allows his students to voice their opinions in class, ______ sometimes their opinions are not sound.

A．so that

B．in case

C．even if

D．as though

三国两晋南北朝时期，中国历史的基本特点是（）

A.群雄并起与国家分裂

B. * * 分立与民族融合

C.民族交往与民族融合

D.经济发展与科技进步