how long 的用法在句子里的用法、

How long+have/has+been+doing?(现在完成进行时态)

how long意为“多久、多长时间”，主要是对一段时间进行提问，答语通常是（for）three days/weeks/months等时间段，它可用于各种时态。
How long do you stay in Beijing every year? 每年你在北京住多久？
How long have they lived here? 他们住在这里有多久了？
—How long were you not at school last year? 去年你多久没上学？
—About two weeks. 约两周。

简单说来就是 "How long"+"动"+"宾"
"How long"有两种意思：
多长-
How long is the Great Wall of China?
中国的长城有多长.
多久（多长时间）-
How long have you been sick?
你病了多长时间了?
How long were you hospitalized for?
你住院以来多长时间了?
用法跟陈述句有关.
如果是说中国的长城有多长,陈述句是：
The Great Wall of China is xxxx kilometers long.
在"How long"的后面加上be动词,再把剩下的句子加上,就是：
How long + "be" + "object" =
How long is the Great Wall of China.
如果是指时间,陈述句是：
You have been sick for a week.
在"How long"的后面加上动词（或助动词/"be"动词）,再加上要问的.如果有助动词,那么助动词在前面,然后是主语,然后是动词+剩下的句子：
How long + "be" + "object" =
How long "have"（助动词）+ "you"（主语）+ "been"（be动词）+ sick?
How long have you been sick?
其实用法同其他问句或倒装句.
希望回答了你的求助.