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

问题补充：

Last year the number of students who graduated with a driving licence 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：句意：去年考过驾照的学生人数达到了20万，平均每年4万。an average of平均是……。