The Diaoyu islands have been part of China's territory since ancient times as important

问题补充：

The Diaoyu islands have been part of Chinas territory since ancient times, as important fishing grounds of Taiwan.

A. served

B. to serve

C. serving

D. having served

答案：

A. served

B. to serve

(答案→)C. serving

D. having served

解析：C 考察非谓语动词。句义：钓鱼岛作为台湾的重要渔场，自古以来就是中国的领土。分析句子结构可知，空格处做伴随状语，且和主语是逻辑上的主动关系，故用现在分词做状语，表示主动关系。故C正确。