It shows that a knowledge of first aid can make a real.A. effectB. effortC. importance　　　D

问题补充：

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

A. effect

B. effort

C. importance

D. difference

答案：

A. effect

B. effort

C. importance

(答案→)D. difference

解析：考查固定结构。Make a difference起作用，有影响。句意：结果显示急救知识真的有很大作用。根据句意说明D正确。