– do I have to take the medicine? – Three times a day after meals.A. How longB. How farC

问题补充：

– do I have to take the medicine?

– Three times a day, after meals.

A. How long

B. How far

C. How often

D. How soon

答案：

A. How long

B. How far

(答案→)C. How often

D. How soon

解析：句意:-我应该多长时间吃一次药？-一天三次，饭后。根据这个情景中的回答three times a day，可知，这里是询问吃药的频率，即多久吃一次，提问频率应该用how often。how long 多长时间，对一段时间提问；how far 多远，提问距离；how soon 多久，多快；how often 多久一次。故选C。