---who is singing and dancing in the gym now?---（it is）the students from the school.--it is none of your buiness （what）other people think about you ,believe yourself.---the floor and the infection （it）brought along really made the village

---who is singing and dancing in the gym now?---（it is）the students from the school.--it is none of your buiness （what）other people think about you ,believe yourself.---the floor and the infection （it）brought along really made the village
---who is singing and dancing in the gym now?
---（it is）the students from the school.
--it is none of your buiness （what）other people think about you ,believe yourself.
---the floor and the infection （it）brought along really made the villagers suffer a lot
---having checked the doors were closed,and（that）all the lights were off ,the boy opend the door to his bedroom.
请问为什么要用括号里的词,而不用（they are） （how）（that）（when）

---who is singing and dancing in the gym now?---（it is）the students from the school.--it is none of your buiness （what）other people think about you ,believe yourself.---the floor and the infection （it）brought along really made the village
1. --- Who is singing and dancing in the gym now?
---（It is）the students from the school.
人称代词不仅用于指代上文中提到过的无生命物体,而且还指代性别不详、不知或不相关的有生命的群体,如：
Is this your book? Yes, it is.
Who is speaking over there? It's Tom speaking. ( 电话用语)
该题中指代的就是不明的有生命的群体.
2. --- It is none of your buiness（what）other people think about you ,believe yourself.
这里的代词 what 是 think 的宾语,如果改为副词 how,必须改为 how other people think it about you, 否则句子缺少成分,不完整.

3. --- The flu and the infection （it）brought along really made the villagers suffer a lot.
这是一个主从复合句,其中：
主句——The flu and the infection really made the villagers suffer a lot.
定语从句——（that）it brought along ,关系代词 that 是从句中 brought 的宾语,因此省略.
4. --- Having checked the doors were closed,and（that）all the lights were off ,the boy opend the door to his bedroom.
本句含有现在分词短语 Having checked ...充当的时间状语,其中包括由 and 连接的两个并列的宾语从句,即：
1）Having checked the doors were closed
2）and (having checked）that all the lights were off
由于第二个从句离开动词较远,为了让人看清它也是动词 checked 的宾语从句,因此用了连接词 that.

第一道：其实they are也不算错，只是不符合平时习惯，通常在不清楚对方情况或不知是男是女时都会这么用的。
第二道：what后面是主语的补语，换过来这个句子就是what...is none of your businese.
第三道还真不清楚
第四道我感觉that是个从句，放在and后时that一般不可省...

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第一道：其实they are也不算错，只是不符合平时习惯，通常在不清楚对方情况或不知是男是女时都会这么用的。
第二道：what后面是主语的补语，换过来这个句子就是what...is none of your businese.
第三道还真不清楚
第四道我感觉that是个从句，放在and后时that一般不可省

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it is 表示你并不一定认识句中所指的人，泛指而已；而they are就不同了。
这句话是说不要介意别人怎么看你，用how似乎没有问题，实际重点是别人对你的看法是什么，（当然是用他们的头脑看法评价你）所以how 是矛盾的，中英文的语意差别。
it 指代floor，这并不是一个定语从句。
男孩是同时检查门已经锁了、灯已经关了才回房的，没有很明显的先后顺序，用when不合适。...

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it is 表示你并不一定认识句中所指的人，泛指而已；而they are就不同了。
这句话是说不要介意别人怎么看你，用how似乎没有问题，实际重点是别人对你的看法是什么，（当然是用他们的头脑看法评价你）所以how 是矛盾的，中英文的语意差别。
it 指代floor，这并不是一个定语从句。
男孩是同时检查门已经锁了、灯已经关了才回房的，没有很明显的先后顺序，用when不合适。

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