— times do you visit your grandparents every year?— Three or four times a year. Usually a

问题补充：

— times do you visit your grandparents every year?

— Three or four times a year. Usually at Mid-Autumn festival and Spring Festival.

A. How long

B. How often

C. How much

D. How many

答案：

A. How long

B. How often

C. How much

(答案→)D. How many

解析：How long多长；How often多久一次；How much多少钱；How many多少个。根据下文，一年三到四次。可知上文提问的是频率，故选D，每年你多久拜访你的祖父母一次？