问题补充：
— do you go to the zoo with your brother?
—Three times a month.
A. How long
B. How often
C. How old
D. How much
答案：
A. How long
(答案→)B. How often
C. How old
D. How much
解析：句意：你和你哥哥多久去一次动物园？一个月三次。根据答语可知上句是提问频率。A多久，问时间段，B多久一次，C多大了，问年龄，D多少，问价格。故选B.
