-do you have an English party?-Once a month.A. How oldB. How farC. How oftenD. How

问题补充：

---- do you have an English party?

---- Once a month.

A. How old

B. How far

C. How often

D. How long

答案：

A. How old

B. How far

(答案→)C. How often

D. How long

解析：How old多大；How far多远；How often多久一次；How long多长；根据下文答语，一个月一次。可知上文提问的是频率，故选C。