问题补充：
— do you visit your grandparents?
—Twice a month.
A. How many
B. How much
C. How far
D. How often
答案：
A. How many
B. How much
C. How far
(答案→)D. How often
解析：How many多少个；How much多少钱；How far多远；How often多久一次。根据下文，一个月两次。可知上文提问的是频率，故选D，你多久拜访一次你的祖父母？
