--do you visit your grandparents?-----Once a month.A How soon B How long C How much

问题补充：

----- do you visit your grandparents?

-------Once a month.

A How soon B How long C How much D How often

答案：

解析：疑问词辨析。How soon多久；How long多长；How much多少元； How often多久一次。根据下文，每个月一次。可知上文提问频率，故选D，你多久拜访一次你的爷爷奶奶？