It shows that knowledge of first aid can make a real difference.A. aB. theC. oneD. /

问题补充：

It shows that knowledge of first aid can make a real difference.

A. a

B. the

C. one

D. /

答案：

(答案→)A. a

B. the

C. one

D. /

解析：考查冠词和代词。句意“这证明掌握急救知识可以有很大帮助。”a knowledge of...“关于......的知识”，是固定搭配。故选A。