It said the country's confirmed H7N9 cases were isolated and there has been no of human-to

问题补充：

It said the countrys confirmed H7N9 cases were isolated and there has been no of human-to-human transmission.

A. mark

B. symbol

C. sign

D. signal

答案：

A. mark

B. symbol

(答案→)C. sign

D. signal

解析：考查名词辨析：A. mark记号B.symbol 象征C.sign迹象D.signal信号，句意：据说这个国家的确认H7N9病例被隔离,没有任何迹象表明人际间的传播。选C。