问题补充：
--do you have PE lessons?
--Three times a week.
A. How long
B. How soon
C. How many
D. How often
答案：
A. How long
B. How soon
C. How many
(答案→)D. How often
解析：考查疑问词。How long多长； How soon多久； How many多少个；How often多久一次。根据答语的内容Three times a week.为一周三次，可知上文提问频率的，故选D
