is clear the Diaoyu islands have been China's inherent territory （固有领土）both from historical and legal aspects since ancient times．
A. That; that
B. This; this
C. It; that
D. What; what
网友回答
A. That; that
B. This; this
(答案→)C. It; that
D. What; what
解析：考查形式主语句。本题的it是形式主语，真正的主语是that所引导的主语从句，that在句中不充当任何成分，只是一个引导词，没有任何的意思。句意:钓鱼岛自古以来就是中国的领土这一点是非常清楚的。故C正确。