搞不懂时态问题，不知道句子该用什么时态，具体说明下
一、一般现在时主要用于：
1 、表示经常性或习惯性动作。
e.g. It seldom snows here.
2 、表示现在的特征或状态。
e.g. He is always ready to help others.
3 、普遍真理。
e.g. Action speaks louder than words.
4 、剧情图片介绍，背景说明，动作解说。
e.g. (Tom enters the room and sits at the table)
Doctor ： What's your trouble, young man?
Tom ： I've caught a cold, doctor.
5 、时间、条件、让步、方式状语从句表将要发生的动作时。
e.g. Tomorrow we shall go for an outing unless it rains.
与这种时态连用的时间状语常有：
always, often, never, seldom, usually, once, a week, now 等。
二、一般过去时主要用于：
1 、表示过去某个时间发生的动作或情况（包括习惯性的动作或状态）
e.g. When did you read the novel?
She often came to help us in those days.
2 、谈到过去的情况时
e.g. I didn't know you were so busy.
3 、谈到已死人的情况时
e.g. Lei Feng was a great communist fighter.
与这个时态连用的时间状语常有：
yesterday, last night, the other day, two months ago, in 1985, then, just now,
when, after, as soon as 引导的时间状语从句，表示主句动作开始的时间。
三、现在完成时主要用于：
1 、表示到现在为止这一时期中发生的动作或情况，即多次动作的总和。
e.g. We have learnt four English songs this month.
How many times have you read the novel?
For many days we haven't seen each other.
2 、表示对现在有影响的某一已发生的动作。
e.g. The delegation has left 代表团已经走了（说明现在不在这里）
Look, what you have done. 看你干的事。
与这一时态连用的时间状语有：
already, yet, just, ever, never, by now, so far, recently, by the end of this month, since, for 短语，连词 since 引导的时间状语从句。
一般过去时与现在完成时的区别：
一般过去时：重在说明动作在过去发生时的具体情况（时间、地点、方式、对象、细节等）。
现在完成时：只提起已发生的动作（事实）及其影响，不说明动作发生时的具体情况。
cf. Have you had your lunch?
What did you have for lunch?
I have ever been to the Great Wall, and I went there last summer with my father.
注：现在完成时表达的动作常具有反复性，故下面一句是错的：
Have you seen the six thirty's news program?
应改为：
Did you see the six thirty's news program?
四、现在完成进行时主要用于：表示过去开始的某一动作一直持续到现在，以至延伸到将来，它强调动作延续时
间之长久。
e.g. I've been writing an article. 我一直在写一篇文章。（还在写）
cf. I've written an article. 我写了一篇文章。（已写完）
It has been raining these days. 这些天一直在下雨。
五、过去完成时
1 、过去完成时是一个相对时态，表示过去的过去，只有在两个过去发生的动作相比较时才可显示出来。
e.g. As soon as we got to the station, the train had left.
注：主从句表达的动作紧接时，即两动作发生的时间没有明显时间上的悬殊或空档时，主从句都可用一般过去时。
e.g. Where did your brother study before he joined the army?
2 、过去完成时可表示截止过去某一时间动作的总或动作的结束。
e.g. By the end of last month. We had reviewed four books
By eight o'clock, he had finished his homework.
与这个时态连用的时间状语常有：
by 1985, by eight o'clock, by then, by the end of last month, by the time when, when, as soon as, before 等连词引导的时间状语从句，表示主句动作结束的时间。
（六）现在进行时主要用于：
1 、表示现在或现阶段正在进行的动作。
e.g. Listen, someone is crying.
What are you doing these days?
2 、代替一般现在时，表示经常性动作或状态，而含有某种感情色彩。
e.g. How are you feeling today?
你今天感觉怎样？（显得亲切）
He is doing well in his lessons.
他的功课很好。（赞扬）
You are always boasting.
你老爱吹牛。（厌烦）
3 、动词 go, come, leave, arrive 等表将要发生的动作时。
e.g. They are leaving for Shanghai.
与这种时态连用的时间状语常有：
now, these days, recently, this week 等。
七、过去进行时主要用于：
表示过去某个时刻或阶段正在进行的动作。
e.g. At that time she was working in a PLA unit.
那时她在解放军某部工作。
What were you doing this time yesterday?
与这个时态连用的时间状语常用：
at nine o'clock, this time last night, these days, at that time 等。
用 when 引导的时间状语从句表示主句的动作正在进行的时间。
e.g. When he came in, I was reading a newspaper.
注：
1 、 while 引导时间状语从句叙述过去的动作时，从句常用过去进行时。
e.g. I read a magazine while I was waiting for the bus.
2 、 when 用作并列连词，意为“这时”，连接两分句时，第一句多用过去进行时。
e.g. I was reading a newspaper when he came in.
一般过去时与过去进行时的区别：
一般过去时：强调过去某一时间开始或完成的动作。
过去进行时：强调过去某一时间正在进行的动作。
试区别下面两句：
We were building a reservoir last winter.
去年冬天我们在修建一座水库。（可能尚未建成）
We built a reservoir last winter.
去年冬天我们修建了一座水库。（已经建成）
八、一般将来时主要用于：
表示将要发生的动作或情况
e.g. Tom will have a bike of his own.
与这个时态连用的时间状语常用：
tonight, tomorrow, the day after tomorrow, next week, in three hours, two days later 等。
一般将来时态与其它结构表将来情况的区别：
一般将来时态 ：主要从时间的角度表将要发生的动作或情况。
be going to 结构 ：①表（主观上）打算或准备做某事时。 ②表有发生某事的预兆时。
e.g. They are going to have a competition with us in studies.
It is going to rain.
据以上区别，故下面一句是错的：
I am going to be eighteen years old next year.
应改为： I shall be eighteen years old next year.
be about to do sth 结构 ：意为“刚要做某事”、“马上要做某事”强调时间之紧迫性。
e.g. We are about to discuss this problem.
我们将马上讨论这个问题。
be to do sth 结构： 表示按计划、安排、规定将实施某事或表示注定会发生某事。
e.g. When is the train to leave.
All these things are to be answered for.
1 、表示经常性或习惯性动作。
e.g. It seldom snows here.
2 、表示现在的特征或状态。
e.g. He is always ready to help others.
3 、普遍真理。
e.g. Action speaks louder than words.
4 、剧情图片介绍，背景说明，动作解说。
e.g. (Tom enters the room and sits at the table)
Doctor ： What's your trouble, young man?
Tom ： I've caught a cold, doctor.
5 、时间、条件、让步、方式状语从句表将要发生的动作时。
e.g. Tomorrow we shall go for an outing unless it rains.
与这种时态连用的时间状语常有：
always, often, never, seldom, usually, once, a week, now 等。
二、一般过去时主要用于：
1 、表示过去某个时间发生的动作或情况（包括习惯性的动作或状态）
e.g. When did you read the novel?
She often came to help us in those days.
2 、谈到过去的情况时
e.g. I didn't know you were so busy.
3 、谈到已死人的情况时
e.g. Lei Feng was a great communist fighter.
与这个时态连用的时间状语常有：
yesterday, last night, the other day, two months ago, in 1985, then, just now,
when, after, as soon as 引导的时间状语从句，表示主句动作开始的时间。
三、现在完成时主要用于：
1 、表示到现在为止这一时期中发生的动作或情况，即多次动作的总和。
e.g. We have learnt four English songs this month.
How many times have you read the novel?
For many days we haven't seen each other.
2 、表示对现在有影响的某一已发生的动作。
e.g. The delegation has left 代表团已经走了（说明现在不在这里）
Look, what you have done. 看你干的事。
与这一时态连用的时间状语有：
already, yet, just, ever, never, by now, so far, recently, by the end of this month, since, for 短语，连词 since 引导的时间状语从句。
一般过去时与现在完成时的区别：
一般过去时：重在说明动作在过去发生时的具体情况（时间、地点、方式、对象、细节等）。
现在完成时：只提起已发生的动作（事实）及其影响，不说明动作发生时的具体情况。
cf. Have you had your lunch?
What did you have for lunch?
I have ever been to the Great Wall, and I went there last summer with my father.
注：现在完成时表达的动作常具有反复性，故下面一句是错的：
Have you seen the six thirty's news program?
应改为：
Did you see the six thirty's news program?
四、现在完成进行时主要用于：表示过去开始的某一动作一直持续到现在，以至延伸到将来，它强调动作延续时
间之长久。
e.g. I've been writing an article. 我一直在写一篇文章。（还在写）
cf. I've written an article. 我写了一篇文章。（已写完）
It has been raining these days. 这些天一直在下雨。
五、过去完成时
1 、过去完成时是一个相对时态，表示过去的过去，只有在两个过去发生的动作相比较时才可显示出来。
e.g. As soon as we got to the station, the train had left.
注：主从句表达的动作紧接时，即两动作发生的时间没有明显时间上的悬殊或空档时，主从句都可用一般过去时。
e.g. Where did your brother study before he joined the army?
2 、过去完成时可表示截止过去某一时间动作的总或动作的结束。
e.g. By the end of last month. We had reviewed four books
By eight o'clock, he had finished his homework.
与这个时态连用的时间状语常有：
by 1985, by eight o'clock, by then, by the end of last month, by the time when, when, as soon as, before 等连词引导的时间状语从句，表示主句动作结束的时间。
（六）现在进行时主要用于：
1 、表示现在或现阶段正在进行的动作。
e.g. Listen, someone is crying.
What are you doing these days?
2 、代替一般现在时，表示经常性动作或状态，而含有某种感情色彩。
e.g. How are you feeling today?
你今天感觉怎样？（显得亲切）
He is doing well in his lessons.
他的功课很好。（赞扬）
You are always boasting.
你老爱吹牛。（厌烦）
3 、动词 go, come, leave, arrive 等表将要发生的动作时。
e.g. They are leaving for Shanghai.
与这种时态连用的时间状语常有：
now, these days, recently, this week 等。
七、过去进行时主要用于：
表示过去某个时刻或阶段正在进行的动作。
e.g. At that time she was working in a PLA unit.
那时她在解放军某部工作。
What were you doing this time yesterday?
与这个时态连用的时间状语常用：
at nine o'clock, this time last night, these days, at that time 等。
用 when 引导的时间状语从句表示主句的动作正在进行的时间。
e.g. When he came in, I was reading a newspaper.
注：
1 、 while 引导时间状语从句叙述过去的动作时，从句常用过去进行时。
e.g. I read a magazine while I was waiting for the bus.
2 、 when 用作并列连词，意为“这时”，连接两分句时，第一句多用过去进行时。
e.g. I was reading a newspaper when he came in.
一般过去时与过去进行时的区别：
一般过去时：强调过去某一时间开始或完成的动作。
过去进行时：强调过去某一时间正在进行的动作。
试区别下面两句：
We were building a reservoir last winter.
去年冬天我们在修建一座水库。（可能尚未建成）
We built a reservoir last winter.
去年冬天我们修建了一座水库。（已经建成）
八、一般将来时主要用于：
表示将要发生的动作或情况
e.g. Tom will have a bike of his own.
与这个时态连用的时间状语常用：
tonight, tomorrow, the day after tomorrow, next week, in three hours, two days later 等。
一般将来时态与其它结构表将来情况的区别：
一般将来时态 ：主要从时间的角度表将要发生的动作或情况。
be going to 结构 ：①表（主观上）打算或准备做某事时。 ②表有发生某事的预兆时。
e.g. They are going to have a competition with us in studies.
It is going to rain.
据以上区别，故下面一句是错的：
I am going to be eighteen years old next year.
应改为： I shall be eighteen years old next year.
be about to do sth 结构 ：意为“刚要做某事”、“马上要做某事”强调时间之紧迫性。
e.g. We are about to discuss this problem.
我们将马上讨论这个问题。
be to do sth 结构： 表示按计划、安排、规定将实施某事或表示注定会发生某事。
e.g. When is the train to leave.
All these things are to be answered for.
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