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how long表示多长时间，与连续性动词连用，主要用于对一段时间进行提问，常用for 时间段回答。
例如：How long did you stay here? I stayed here for two weeks.
how long 还可以表示东西有多长
例如：How long is the river? About 40km.
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How often主要强调动作发生的频率。（做了几次）如果句子中有always, usually, often, never, once a day, twice a week, three times a year等词时，常用how often 提问。
例如：How often does your brother go home? Twice a year.
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how soon指再过多久， 主要对表示将来的时间进行提问，比如：in an hour, in three weeks
例如：How soon will your father be back? In two weeks.
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how far 意为：多远，对距离进行提问
例如：How far is it from your home to school? About four kilometers.
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加强训练
共同选项：A. How far B. How long C. How soon D. How often
(1) —______ will you come back? —In half an hour.
(2) —______ can I keep the book? —For only a week.
(3) —______ do you visit your parents? —Once a month.
(4) —______ is the road? —Three kilometers.
(5) —______ is the road from your school? —Three kilometers. / Ten minutes’ walk.
(6) —Do you know ______ we will take part in the High School Entrance Exam?
—Look at the blackboard. There are only forty days left.
答案：CBDBAC
