— do you have an Art Festival in your school?
— Once a year.
A. How long
B. How often
C. How far
D. How soon
网友回答
A. How long
(答案→)B. How often
C. How far
D. How soon
解析：
根据答语once a year可知问的是频度，how often多久一次符合题意，故选B。how long问的是时间或物体的长度；how far问的是距离；how soon问还过多久，都不对。