in 后面必须加the吗？

in的后面加不加the啊~

首先与词性无关
其次the是冠词（a an the）里的定冠词，多用于修饰一些专有名词例如：the Palace Museum故宫,the Great Wall长城等可是它还能用在一些词组中，比如in the morning,in the afternoon,in the evening等就属于固定搭配。
然而in public 这种固定词组不能加。你只要积累这种固定用法，就能找到规律了。
你真是一位认真的好学生！祝你不断进步！

后面跟名词时，都要加呀！

不是必须。

in是介词，介词后面必须接名词，代词或者动名词，即doing。
当介词in单独使用时，或者与其它动词构成固定搭配时，都不能脱离其作为介词的特点。

in 常用意思：在..., 在...之内，从事于..., 按照..., 穿着...。
He was born in 1992. 他生于1992年。
I could finish the program in two weeks.我可以用两周时间完成这个项目。
He spend less time in reading.他读书时间很少。
The man in black jacket is our teacher.穿黑夹克的那个人是我们的老师。

一些与介词in的固定搭配，供参考：

表示时间

in 1999, in 20 century, in a flash(瞬时), in a lucky hour(在幸运时刻), in a minute, in a second, in a short time, in a while, in a wink(一瞬间) in advance(预先), in an emergency(在紧急地时候), in an evil hour(在不幸地时刻), in an instant, in ancient times, in broad day(在大白天), in course of, (在…期间), in December, in due course(及时地), in future, in good season(及时地), in no time(马上), in one”s childhood, in one”s spare time, in one”s teens, in one”s youth, in recent years, in season(适时), in seconds(在很短的时间), in some cases(有时候), in spring, in the afternoon, in the beginning, in the daytime, in the end, in the evening, in the future, in the long run(最后), in the meantime, in the morning, in the nick of time(在紧急关头), in the night, in the past, in the thick of (在最激烈的时刻), in the thick of(在最激烈的时刻), in this period, in those days, in time of war, in time，

表示地点

in a car, in a queue, in advance of (在…前面), in all the direction, in appearance, in corners(在角落里) in doors, in front (of), in good light(在光线好的地方), in heaven, in place(position)(在适当地位置), in places(处处), in port(在港内), in public places, in shore(靠岸), in society, in the air(在空中) in the bank, in the book(书的内容里), in the centre(在中央), in the countryside, in the distance(在远处那边), in the east of(在…东部) in the east, in the fields, in the film, in the front rank(在前列), in the front row, in the lab, in the letter(信的内容), in the middle of, in the moonlight, in the newspaper(报纸的内容里), in the open air(在户外), in the open(在野外), in the picture, in the rain, in the room, in the shade of, in the sky, in the suburbs of, in the sunshine, in the tree, in the universe, in the vicinity of(在附近), in the warm(在暖和的地方) in the world, in(on) the bus, in(on) the street,

表示状态

in progress(在进行中), in a dilemma(处于进退两难的境地), in a hurry, in a tight corner(处于困难中), in action(在行动中), in an emergency, (处于紧急情况中), in anxiety, in astonishment, in bad mood(心情不好), in bad temper(心情不好，生气), in bed, in blossom(bloom) (在开花 ), in bonds(在拘留中), in chains(在囚禁中), in charge(看管), in church, in class, in collision(在冲突中), in commission (在服役), in condition(健康情况良好), in confusion (在混乱中), in control (of), in court(出庭), in custody(拘留), in danger, in debt(负债) , in deep water(s)(处于困境), in demand(有需求) in despair, in difficult, in dispute(在争论), in doubt, in employment, in exile(在流放), in fear and trembling(提心吊胆), in flight(飞行), in flood, in full blossom(开着花), in good condition, in good health, in high spirits, in horror, in hospital, in isolation. in love, in

motion, in need (of) in operation(在运转), in order(状态良好), in panic, in peace(平安)(at peace和平), in peril(处于危险), in place, in power, in practice(在实践中), in preparation, in process(在进行中), in production, in progress(前进，进行中), in pursuit(在追赶中), in question(正被讨论), in rehearsal(在彩排), in retirement(退休), in retreat(在撤退) in sail(张着帆) in secret, in service, in session(在会议中), in short supply, in silence, in sorrow, in stock(有库存) in store(储藏着) in succession, in surprise, in suspension(悬浮中) in tears(流着泪) in the field(在作战), in the press(在印刷), in the red(负债), in the same boat(处境相同), in the works(在计划中), in thought, in trade, in triumph, in trouble, in use, in view(被考虑), in wonder, in work(有工作), in work, in(at) college, in(at) school, in(at) university,

希望能帮到你

不是 the 就是一个特指 这个的意思 比如 在你的桌子下面 就用 under your desk 后面全都类似

in your desk 是说在你的桌子里面 on 指...上面 under 指...下面（正下方）

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建宁县19833968258： in加科目时加the吗?eg:I get good grades in - 我应该加? - ？
岳泊因卡： 不用加the 这个后面可以跟的有很多 比如science Maths Chinese English Chemistry

建宁县19833968258： 在in后面加the或者不加the有什么不同?关于使用的对象什么的…… - ？
岳泊因卡： 则只是一个简单的状语 只表示动作发生的时间 而不强调这个时间有什么不同 在春天-in the spring 另外,当季节是特指时,要加定冠词the . 如:在

建宁县19833968258： in 后面必须加the吗?为什么in your desk是对的呢?on,under呢? - ？
岳泊因卡：[答案] 不是 the 就是一个特指 这个的意思 比如 在你的桌子下面 就用 under your desk 后面全都类似

建宁县19833968258： 在in后面加the或者不加the有什么不同?关于使用的对象什么的……如上. - ？
岳泊因卡：[答案] 加THE 表示在内部,不加在外部.比如: in the front of the classrooom和in front of the classroom.前者是在教室内部的前面,好比讲台.后者是教室外部的前面,比如说教室外边前面的石碑.

建宁县19833968258： 英语介词in什么时候后面加the什么时候不加the? - ？
岳泊因卡： 表示特指或一些固定短语,如in the desk(特指), in the evening (固定短语)

建宁县19833968258： at home 为什么不用in 举例说明 如果用in 后面要加the吗 - ？
岳泊因卡： 记住两个常用短语:at home in one's family

建宁县19833968258： in后面什么时候要加the,急求! - ？
岳泊因卡： 什么时候要加 an ,什么时候要加 a . 是 the 后面的词 什么时候要加 the, 什么时候不要加 the 不是in 后面什么时候加 the 的问题

建宁县19833968258： 什么情况下in后面加the - ？
岳泊因卡：[答案] 地方较小,比如in the library,in the classroom,school,而大的,例如国家就不加the

建宁县19833968258： 关于in 后面加国家的用法 - ？
岳泊因卡： the.USA要加,UK(英国)就不加,但UK的全称The United Kingdom of Great Britain and Northern Ireland就要加,PRC.中华人民共和国也不加.只有靠记忆,都是固定搭配. in表示一个时期. in后常接年,月,日期,上午,下午,晚上,白天...

建宁县19833968258： 在in the morning中为什么in后面要加the呢?在in spring中in和spring中为什么不加the??? - ？
岳泊因卡： 这是个固定用法 一年四季的单词前面都不加the的 而早上晚上都加the,for instance:in the afternoon,in the evening 但是也有特殊 at noon ,at night 记住就可以了 没有多大的语法在里面