问题补充：
-do you spare time to visit your parents every month?
-Twice.
A. How long
B. How often
C. How soon
D. How fast
答案：
A. How long
(答案→)B. How often
C. How soon
D. How fast
解析：考查特殊疑问词。根据下文的twice，说明是对频率进行的提问。故使用how often, how long是对一段时间进行提问。How soon是对将来时进行提问。故B正确。
