by + 时间点用于什么时态

The park is open at 7:00,and it's closed at 3:00.

应该是on an interesting sunday,其实这要看情况而定，具体日期，如：sunday,monday,july 1st,等就用on。如果只有年月的就用in。in+一段时间表示将来时的什么时候之后，如一小时以后（表将来）：in one hour。at后面一般加某个时间点，如在二点：at two o'clock

时间段,凡是介词用in的都是时间段,大时间点的介词为on（指具体某一天）,小时间点的介词用at（指集体几点几分）
when可以提问时间段和点,what time只能提问时间点,而且还是小时间点.

不能,现在完成时只能与表示时间段的词或词组连用

What time 对较具体的时间提问
When对大时间提问

以你的这个句子为例说明吧
“I was watching TV when my mother came back."
这个时间状语从句涉及到两个动作,一个是"我在看电视",一个人是"妈妈回来"
由于"我在看电视"是一个持续性的动作,　"妈妈回来"是一个短暂性的瞬间动作,所以"我在看电视”用的是过去进行时,表示一个连续的状态；"妈妈回来"用的一般过去时,动作瞬间结束了.
一般来说,记住持续性的、连续状态的用进行时态（am/is/are/were/was+doing）即用到Be 动词；短暂的瞬间的动作用用do/did的基本形式即可.

in+ 一段时间,常与一般将来时连用.
after +时间点,与一将来时连用； after+ 一段时间,与一般过去时连用.
for + 一段时间,多与现在完成时连用.如
He will come back in two days.
She will come home after two o'clock .
After a while ,he went out without saying a word.
He has studied at this scholl for two years.
加油!不明白再问!

可以，这个叫直接引语， 是没有问题的。与其对应的是间接引语，具体的内容自己百度间接引语和直接引语就好了

A Chen and late
B this is the Chinese and Western concept of time difference
A westerners is a point in time,while Chinese is a time period
B so we might arrived earlier than you,also may be late,but the late often will be more.
A to B,this is very interesting and you have not found,
A self awareness is also different in Chinese and Western culture and I think Chinese more introverted,not confident
B relative you Westerners are confident,have a strong sense of self
A this should be the historical system and the problem of belief.
B I think so too.

表示时间点有at
表示时间段有for, in

what time
如 I often get up at six
what time do you often get up?

自从两年之前,是时间段,意思是从两年以来一直持续某种状态.

I have been a PLA man since I finished the college. 说的就是这情况。

since+过去某一时间或句子,for+一段时间
She has taught in the school for ten years.她在这所学校教书已经10年了.
I haven't eaten anything since breakfast.我从早饭起就一直没有吃东西.

进行时应该不能表示时间段,完成进行时可以

5：00 watch a soccer match with English commentation
8：00 watch a basketball match with English commentation
15：00 play soccer
17：00 play tennis
19：00 play basketball
21：00 watch tennis

since加时间点,时间点的时态应该是过去时,整句话应该是现在完成时.
例如：I have lived here since ten years ago.自从10年以前我就住在这里.
He has been in Beijing since 2000.自从2000年他就去北京了.
ten years ago 和2000 都属于过去的时间点.

完全正确。for和since引导的时间状语都修饰延续性动词。

时间段 since+时间点

一段时间,in a week可以理解为在一周以内,比如常用的是在别人催促的时候可以说in a minute 就是马上,一分钟以内的意思

5year ago 时间点 ，5 years时间段

这个是你们经常遇到的词组,给你解析一下
how often是对频率的提问.比如how often do you write to your father?
how soon是对即将要到来的事的提问.比如how soon he will come?
how long是对长度或者时间跨度的提问.比如how long did he watch TV last night?
how far是对距离的提问.how far is it from here?

时间点
如：
The Great Wall can date from 2500 years ago.
楼上是忽悠专家!

先把概念搞清楚.酶活力指酶催化反应的能力,活力越高反应越快.但反应速度还与底物和产物的浓度有关,并非仅仅由酶活力决定.至于底物和产物浓度,还与反应时间有关.比如做酶切实验,一开始,酶活力最高,底物浓度也最高,反...

理论上是以飞机落地时间为准,但飞机不像火车,这个时间只供参考,一般不会那么准时的

都可以出.洛溪站往嘉禾望岗方向,23：34关站（尾班车23：39）,所以你只要坐上23：00前（你所说的十点多）,都可以到达海珠广场、公园前站.也就是说你到达这两个站的极限最晚到洛溪站的时间是23：34分.
由于公园前1号线往广州东站方向,23：10分尾班（即23：05分关站）,所以,如果你要到农讲所,你必须在22：35前到达洛溪站,才能确保你坐上1号线,去往农讲所.也就是说22：35是你从洛溪出发去往农讲所的极限最晚时间.
明白吗

请问你的加速度随时间变化是连续的还是一些离散的数据呢?
如果是离散的数据的话应标t1~t2加速度是a1,t2~t3是a2……,公式中积分应换成取和Σ,a换成a(n-1),dt换成t(n)-t(n-1)
如果是连续的数据,先列微分算式：
dv=adt,看a和t满足什么关系,即求出函数a(t),然后代入,做定积分

应该是公元1500年

过去完成进行时,had been studying.

at the end of和by the end of都可以加时间段的,例如Are there any examinations at the end of term?学期结束时有考试吗?其中terms的含义就是学期,可以说是一段时间.We shall finish the civil work by the end of the year.在年底前我们将完成土建工作.其中的the year其实也是一段时间的.区别其中的含义是比较重要的,不能单纯说哪个加时间段或者时间点.at the end of在…结尾,在…末端,后面可以加一个名词,除了时间外还可以加表示事物或者地点的名词；by the end of到…为止,后面也是可以加一个时间名词,如the year,the day,the month等等,如果硬要说时间点或者段的话,则at the end of就是时间段喽,by the end of也是接时间点喽!by the end of一般都是加的时间名词,翻译过来就是到某个时刻为止,如果是到某个地点或者事物为止,意义就不符了,那么此时at the end of就更加符合意思了,也就是在某个位置的结尾,时间的末端或者某个地点的转弯处.

意思是：在...时候,到...的时候例如：I will finish my homework by five o'clock.我会在五点时完成作业.The light will be turned off by then.到那个时候灯会被关掉.谢谢您的支持!

在时间方面,by是到...为止, in是在这段时间之内
所以这题选by,题意如有一天想起说的
如果是选in的话,后面应该是一段时间,如in 4 hours.在4小时内看完
不过楼上的都对啊

时间段 可以

要知道路程就要算出速度时间图像某个时间点或者几秒内的面积,位移就直接速度时间求积分

2002是个时间点,而since 2002 翻译成从2002年以来,那么since 2002 就是时间段了[参考搭配1]
since 7 days ago中的7 days 是时间段[参考搭配2]
since的搭配有四种
1.since +过去一个时间点 (如具体的年、月、日期、钟点、1980,last month,half past six).
I have been here since 1989.
2.since +一段时间+ ago
I have been here since five months ago.
3.since +从句
Great changes have taken place since you left.
4.It is +一段时间+ since从句
It is two years since I became a postgraduate student.

当然不一定要有.通常表示时间的词汇作为句子的状语成分.
而一个完整的句子通常只要有主谓宾（或主系表等等）成分即可.
比如：She went home.- 她回家了.
Tom got a fever.- 汤姆发烧了.
不明白可继续提问.
若回答对您有所帮助,请点击本页面中的“选为满意回答”按钮,

年限
niánxiàn
[fixed number of years]∶规定的或作为一般标准的年数
学习年限
[life]∶某物适于使用或有效地完成其职能的时间
延长农具的使用年限

three days就是段,three days ago就是点.你可以这么理解,for后面是接一段时间,例如从星期一到星期四.since接点时间,例如星期一这天.

可以搜 英语语法网,上面有个“动词时态”的栏目,讲得很清楚.

for加段时间 表示一个时间段 所以句中的动词也应该是延续性动词 或者类似延续性的 什么时态没区别 since 的用法真的比较复杂 1) since +过去一个时间点

过去式,过去进行时,过去完成式

可以使用过去进行时,不过时态要体现在谓语动词上,所以就算改也要改成：...everything was beginning to shake
began to shake 改成 began shaking 也可以,但这是因为 begin to do sth = begin doing sth,并不是因为改用过去进行时的原因.

“时间点”是相对于“时间段”而言的.

时间点是表示某一瞬间的具体时间,如9点.英文为at nine o'clock等

时间段是从一个时间点到另一个时间点,如3点到5点这段时间或1天,1个星期等.如in spring 在春天；in 2014 在2014年等

时间段

Since 用来说明动作起始时间,for用来说明动作延续时间长度.
I have lived here for more than twenty years.
I have lived here since I was born..
My aunt has worked in a clinic since 1949.
Some new oilfields have been opened up since 1976.
I have known Xiao Li since she was a little girl.
My brother has been in the Youth League for two years.
I have not heard from my uncle for a long time.
注意：并非有for 作为时间状语的句子都用现在完成时.
I worked here for more than twenty years.
(我现在已不在这里工作.)
I have worked here for many years.
(现在我仍在这里工作.)
小窍门：当现在完成时+一段时间,这一结构中,我们用下面的公式转化,很容易就能排除非延续动词在完成时中的误使.
1) (对) Tom has studied Russian for three years.
= Tom began to study Russian three years ago,and is still studying it now.
2) (错) Harry has got married for six years.
= Harry began to get married six years ago,and is still getting married now.
显然,第二句不对,它应改为 Harry got married six years ago.或 Harry has been married for six years.

since的用法主要有两点：一是表示“自从……以来”,二是表示“既然”之意.但如果只了解词的含义,而不了解其用法,在使用时就会造成错误.例如：I have not heard from him since I lived in Shanghai.不少人会望文生义,将该句译为：“自从我住在上海以来,就再也没有收到他的信了.”而实际上这个句子的译文并非如此,那么正确的含义是什么呢?下面谈谈since作连词引导时间状语从句的用法.一、若since引导的状语从句的谓语动词是终止性的过去时,则从句表示的时间是“从动作开始的那一时刻起”.如：He has studied very hard since he came to our school.自从他来到我们学校,他学习就非常努力.We have been missing them since they left here自从他们离开这里,我们就一直很想念他们.这是最常见的一种用法,此处不再多述.二、若since引导的状语从句的谓语动词是持续性动词或表示状态的动词的过去时时,则从句表示的时间是“从那持续动作或状态结束时算起”.如：I haven’t heard any noise since I slept.Sleep 为持续性动词,sleep的动作结束时,即“醒来”时,这句应译为“我醒后还未听到任何声音”.John is now with his parents in New York,it is already three years since he was a teacher约翰现在和父母一起住在纽约,他不当教师已经三年了.本文开始出现的那个句子就可以译为“自从我离开上海,就再也没有收到他的信.”这种译法常被人们误用,我们不妨再多举几个例子看看：How long is it since you lived in Shanghai?你离开（没住在）上海多久了?It is half a month since he was a League member.他离开团队（不当团队成员）半个月了.It’s been quite some time since I was last in London我离开伦敦已很长时间了.比较：He has written to me frequently since I was ill.自从我病愈以来,他屡次给我写信.（从句谓语为状态动词） He has written to me frequently since I fell ill.自从我生病以来,他就屡次给我写信.（从句谓语为终止性动词） 三、若since引导的状语从句的谓语为持续性动词的现在完成时,则表示动作和状态延续到现在（说话时刻）,其表示的时间的起点应从动作发生之时算起.如：I haven’t heard from him since he has lived there.这里has lived表示动作的持续性,时间的起点应从：“开始居住”时算起.因此此句可理解为“自从他（开始）住在那儿起,我就一直没收到他的来信”.Since we have owned a car,we have gone camping every year.自从我们自己有了汽车,我们每年都去野营.试比较：1.Since I’ve been at this school,we have had three headmasters.自从我到这所学校,我们已换了三个校长了.Since I was at this school,they have had three headmasters.自从我离开这所学校,他们已换了三个校长了.2.He has never been to see me since I have been ill.自从我生病以来,他从未来看过我.He has never been to see me since I was ill.自从我病愈以来,他从未来看过我.由此可见,since引导的从句持续动词的一般过去时和现在完成时所表示的意思恰好相反.换言之,前者以肯定的语法形式反映着否定的逻辑内容,而后者的形式与内容是一致的.至于It is +一段时间+since…的句型与It has been +一段时间+since…意思相同.前者是规范说法,后者是口语说法.应注意的是,在这种结构中,since引导的从句绝对不能用否定式的谓语动词来表示否定意义,下面两句都错了：It is a long time since he didn’t study English.It’s two months since you didn’t come to see me.正确的说法为：It’s a long time since he studied English 他好久没学英语了.You haven’t come to see me for two months.你有两个月没来看我了.

首先,完成式的时间状语是比较明显的是for+时间段、since时间段ago
for+一段时间本来就是表示完成式的,不用ago来,只有since+时间段才需要ago来修饰.
例：I have graduated from high school for 3 years.完成式
I have graduated from high school since 3 years ago.完成式
I graduated from high school 3 years ago.过去式
如果有for+时间+ago的完成式句型不知能否让我开开眼,我貌似还真的没有见过.

熔点是固体将其物态由固态转变（熔化）为液态的温度,一般可用Tm表示.进行相反动作（即由液态转为固态）的温度,称之为凝固点.与沸点不同的是,熔点受压力的影响很小.而大多数情况下一个物体的熔点就等于凝固点.所以熔点指的是温度点,且晶体的熔点一般就只有一个.

在你目前的学习阶段,这样理解基本可以.但要记住,语言是活的,千万不要用这两条来套你的英语应用.