-- do you eat fast food?
--Twice a week.
A. How long
B. How soon
C. How often
D. How far
网友回答
A. How long
B. How soon
(答案→)C. How often
D. How far
解析：考查情景交际。句意：--你多久吃一次快餐？--一周（吃）两次。how long对时间长短提问，与完成时连用；how soon多久以后，与将来时连用；how far对距离提问；根据答语可知，问的是频率，对频率提问，用how often。故选C。