-have you been studying at school?----For more than four yearsA. How oftenB. How long

问题补充：

---- have you been studying at school?

----For more than four years．

A. How often

B. How long

C. How old

D. How far

答案：

A. How often

(答案→)B. How long

C. How old

D. How far

解析：How often多久一次；How long多长；How old多大；How far多远。根据下文，大约超过四年。可知上文问的是时间长短，故选B。