Last year the number of students who graduated with a driving license reached 200 000 a(n

问题补充：

Last year the number of students who graduated with a driving license reached 200,000, a(n) of 40,000 per year.

A. average

B. number

C. amount

D. quantity

答案：

(答案→)A. average

B. number

C. amount

D. quantity

解析：短语辨析。An average of 平均；句意：去年取得驾照的毕业生的数量达到了20万，平均每年4万。