问题补充：
--- Jenny, do you visit your grandparents?
--- Twice a month.
A. How long
B. How soon
C. How often
D. How many
答案：
A. How long
B. How soon
(答案→)C. How often
D. How many
解析：A. How long多长时间 B. How soon 多久 C. How often多久一次D. How many多少；句意：珍妮，你多久去看望你的祖父母一次？一个月两次。故选C
