The American girl has a good of Chinese and can express herself freely in the language.A.

问题补充：

The American girl has a good of Chinese and can express herself freely in the language.

A. item

B. series

C. command

D. usage

答案：

A. item

B. series

(答案→)C. command

D. usage

解析：本题的含义是那个美国女孩很好的掌握了汉语，能够轻松自如的用汉语表达，command表示掌握的意思，故本题选C。