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。