Last year the number of students who graduated with a driving license reached 200,000，a(n) of 40,000 per year.(2010·江西)
A. average
B. number
C. amount
D. quantity
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(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意为“平均数”。