一、how long的用法how long有以下两个主要意思：1.表示多长时间，主要用来对一段时间(如three days, four weeks 等)提问。Eg: I have been here for five months.How long have you been here?2. 表示某东西有多长。如：A：How long is the river? 这条河有多长？B：About 500 km. 大约500千米。二、how often的用法how often 指每隔多久，主要用来对频度副词或 状语(如：once a week, three times a month 等) 提问。如：They come to visit me once a week.How often do they come to visit you?三、how soon的用法how soon 指再过多久，主要用来对表示将来的 一段时间(如：in an hour, in two weeks 等)提问 。如：He will be back in an hour.How soon will he be back?四、how far指提问距离多远It is 4 kilometers from Beijing to Xian.How far is it from Beijing to Xian?