1.how long指多长时间，主要用来对一段时间(如three days， four weeks 等)提问。how long的答语通常是（for）three days/weeks/months等时间段。
例如：
“How long did he stay here?” “About two hours.” “他在这儿呆了多久?”“大约两小时。”
How long have you been in your present job?
你干现在这工作多长时间了？
How long did you spend on your homework?
你做家庭作业用了多长时间？
How long do you think this storm will last?
你看这暴风雨会持续多久？
How long can a human being go without sleep?
人不睡觉能活多久？
How long have you been living in this country?
你在这个国家居住多久啦？
How long will it take her to swim the Channel?
她游过英吉利海峡得用多长时间？
How long can you balance on one leg?
你单腿能站多久？
How long a stay did you have in mind?
你原打算待多长时间？
How long has he been in office?
他任职多久了？
How long have you been studying English?
你学英语多久了？
以上例句摘自《牛津高阶英汉双解词典》
How often do you go to the dentist?一I go every six months.
你多久去看一次牙齿?——我每6个月去一次。
表示长度：
Do you know how long is the yantze river?
你知道长江有多长吗？
How long is the journey to the Great Wall?
去长城的路程有多长？
2.how often指多久一次，主要用来对频度状语(如once a week等)提问。
例如：
How often do you use the bus?
你多长时间坐一次公共汽车？
How often do you go to church?
你多久去教堂做一次礼拜？
How often do you go to the theatre?
你多久看一次戏？
How often do you go swimming?
你多久去游泳一次？
How often do you go riding?
你多长时间骑一次马？
‘How often does it need to be changed?’ — ‘Haven’t the foggiest.’
“大概要多久换一次呢？”——“我一点儿概念也没有。”
以上例句摘自《牛津高阶英汉双解词典》
How often do you brush your teeth?
你多久刷一次牙？
《柯林斯高阶英汉双解学习词典》
How often should I take this medicine?
我应该多长时间吃一次这种药？
How often is the trash and litter cleaned up in your town?
你们镇上的垃圾多久清理一次？
No matter how often they turn up, their welcome never wears out.
不管他们多久露面一次，都永远那么受欢迎。
《柯林斯高阶英汉双解学习词典》
No matter how often they were urged, they could not bring themselves to join in
就算别人说破了嘴皮，他们就是不加入。
《柯林斯高阶英汉双解学习词典》
3.how soon指要多久以后，多快；主要用来对表示将来的一段时间(in an hour， in two weeks 等)提问。问多久时间后动作才会发生的意思即问解决事情等的速度。
例如：How soon can you come?你多快能赶来?
How soon can you get here?
你什么时候能赶到这儿？
A: How soon will you come back?
A：你多久回来?
中考真题- 2016 陕西 情景对话B
How soon can you come up with the money?
你什么时候能拿出这笔钱？
《牛津高阶英汉双解词典》
How soon will the meeting begin?
会议多久以后才开？
How soon is the next train to Hangzhou?
下一班去杭州的火车要多久？
How soon can you let me have a written report?
你多久能给我一份书面报告？
How soon can you get hold of that young man?
你多快可以找到那个年轻人？
How soon shall we know the results? 一I don’t know. 我们多久能知道结果? —我不知道。
How soon will he be back?—In an hour. 他要多久才回来?—1小时以后。
How soon will you be / have finished, dear? 亲爱的，你还要多久才能准备好呢?
How soon will you know your holiday dates? 你什么时候才能知道休假日期?
how soon意为“还要多久”常用在一般将来时态的句子中，其答语通常是“in + 一段时间”。
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