Last year the number of studects who graduated with a driving licence reached 200,000, a(n) of 40,000 per year.
A. average
B. number
C. amount
D. quantity
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(答案→)A. average
B. number
C. amount
D. quantity
解析：an average of平均 a numberof 很多 an amount of 数量（修饰不可数名词）
a quantity of很多，句意“去年考取驾照的学生数达到200000平均每年40000”，答案A。