问题补充：
do you go swimming ? Sometimes.
A. How often
B. How long
C. how many
D. How old
答案：
(答案→)A. How often
B. How long
C. how many
D. How old
解析：A. How often多久一次，表示频率；B. How long 多长时间或是距离 ；C. How many多少，修饰可数名词的复数形式；D. How old多少岁，询问年龄；句意：你多长时间游一次泳？有时。故选A.
