1. how long

　　指多長時間，主要用來對一段時間(如three days, four weeks 等)提問：

　　How long ago was it? 這是多久前的事了?

　　How long do you think you’ll be gone? 你想你會離開多久?

　　How long have you known her? 你認識她有多久了?

　　How long have you been studying the problem? 這問題你研究多久了?

　　“How long did he stay here?” “About two hours.” “他在這兒呆了多久?”“大約兩小時?！?/p>

　　
2. how often

　　指每隔多久，主要用來對頻度副詞或狀語(如once a week等)提問：

　　How often does he come here? —Once a month.

　　他(每隔)多久來一次? —一每月一次。

　　How often do you visit your mother?一Once a week.

　　你多長時間看你媽媽一次?——一周一次。

　　How often do you go to the dentist?一I go every six months.

　　你多久去看一次牙齒?——我每6個月去一次。

　　
3. how soon

　　指再過多久，主要用來對表示將來的一段時間(如in an hour, in two weeks 等)提問：

　　How soon can you come? 你多快能趕來?

　　How soon shall we know the results? 一I don’t know. 我們多久能知道結果? —我不知道。

　　How soon will he be back?—In an hour. 他要多久才回來?—1小時以后。

　　How soon will you be / have finished, dear? 親愛的，你還要多久才能準備好呢?

　　How soon will you know your holiday dates? 你什么時候才能知道休假13期?