这三个疑问词都是用来对时间提问的，但他们在含义和用法上是有区别的。How often有“多久一次”的意思。当对频率提问时，我们常用How often。频率副词和短语有often, sometimes, usually, once/twice/three times a week等。 e.g How often do you watch TV? 你多长时间看一次电影? How long是提问某物“多长”，也可以提问某延续性动作持续“多长时间”。 e.g How long is the stick? 这根棍子有多长？ How long have you lived here? 你住在这里多久了？ How far 是提问“路程有多远” e.g How far is it from his house? 距离他家有多远？ How soon是提问再过“过多久就做某事” e.g How soon will Mike come back? 迈克多过久就回来呢？
how often是多久一次 问频率的 如: how often do you visit your grandparents? once a week. how long 指时间的长度, 或河流的长度, 如: how long can i keep this book? for four weeks. 这本书我能借多久? 四周 how far指距离, 如; how far it from here? 离这多远? how soon是多久以后 也是时间 如how soon does the train leave? 火车什么时候开?