问题补充：
— do you clean your room?
—Every two days.
A. How soon
B. How long
C. How much
D. How often
答案：
A. How soon
B. How long
C. How much
(答案→)D. How often
解析：考查疑问词：A. How soon多久一次，B. How long多长时间，C. How much多少， D. How often多久一次，根据答语的内容Every two days，可知答案为D，表示多久···一次。故选D
