问题补充：
The Australian boy has a good of Chinese and can communicate with others freely.
A. request
B. command
C. demand
D. usage
答案：
A. request
(答案→)B. command
C. demand
D. usage
解析：此处request要求；command命令；demand要求； usage用法。这里have a command of意为：掌握。故选B。句意：这位澳大利亚男孩掌握了汉语并能用汉语和别人自由的交流。
