问题补充：
--- have you been in class today? ---For two hours.
A. How often
B. How long
C. How many
D. How soon
答案：
A. How often
(答案→)B. How long
C. How many
D. How soon
解析：How often多久一次;How long多长,多久;How many多少个;How soon多久,提问将来时间.根据下文,两个小时.可知上文对时间长短进行提问,故选B,今天你上课多久了?
