-do you brush your teeth?--Twice a day.A .How much B. How often C. How long

问题补充：

---- do you brush your teeth?

----- Twice a day.

A .How much B. How often C. How long

答案：

解析：How much多少钱；How often多久一次；How long多长。根据下文，一天两次。可知上文提问的是频率，故选B，你多久刷一次牙？