how often
指“每隔多久,多久一次做。。。”，主要用来对频度副词或状语(如：once a day, three times a week 等)提问。
如：A：How often does he come here? 他(每隔)多久来一次?B：Once a month. 每月一次。
A：How often do you visit your mother? 你多长时间看你妈妈一次?B：Once a week. 一周一次。
how often用来提问某动作或状态发生的频率，对“一段时间内发生了几次活动”（always，usually， often， never或twice a day等表示频度的词或短语）提问时用；
eg:How often do his parents let him watch TV?他父母多久让他看一次电视？
对于how often 的句型回答，一般有这些词表示频率：once,twice,three times,four times,everyday等等。
