高清喷墨瓷砖的优缺点:我不是很了解一般过去时和过去完成时有什么区别？谢谢

1)一般过去时主要用来表示特定过去时间中一次完成的动作或一度存在的状况，其动作或状态已成为过去，现在已不复存在。从其动作的完成到现在之间有一段时间间隔。
一般过去时在特定的句型中表示现在或将来。want, wonder, think，hope用过去时表现在，语气更加委婉。
在wish或it is time从句后用一般过去时表将来，是习惯用法。
例:
He sold newspapers for a living.
他卖报为生计。
He lived in Shanghai for 2 years.
他在上海居住了2年。(现在已不在上海)
－Did you want me?
—你找我吗？
－Yes, I wondered if you'd help me.
—是的，我不知道你能否帮我忙。（委婉语气）

2)过去完成时的主要用法是表示两个事件中哪一个发生在前，表示过去的过去用过去完成时，常和when, after, before, as soon as, by the time that等一起使用。离现在时间最近的动作用一般过去时，表示依次发生在过去的动作应用一般过去时，若有时间间隔，又强调动作的先后概念，宜用过去完成时。
过去完成时常用于间接引语结构中，表示时间向更遥远的过去后移，即通常所说的“过去的过去”。
例:
I told her the parcel had not arrived.
我告诉她包裹还没到。
When we bought it, the house had been empty for several years.
那房子我们买下前，已空置好几年了。
He had died in 1920, before his son was born.
他死于1920，早在他儿子出生以前。

对，都表达的是晚饭前完成作业，区别在于

1）过去时表示过去某时发生的动作或单纯叙述过去的事情，强调动作；现在完成时为过去发生的，强调过去的事情对现在的影响，强调的是影响。

2）过去时常与具体的时间状语连用，而现在完成时通常与模糊的时间状语连用，或无时间状语。

一般过去时的时间状语:
yesterday, last week，…ago, in1980, in October, just now, 具体的时间状语

共同的时间状语:
this morning, tonight,this April, now, once，before, already, recently，lately

现在完成时的时间状语
for, since, so far, ever, never, just, yet, till / until, up to now, in past years, always,
不确定的时间状语

3）现在完成时可表示持续到现在的动作或状态，动词一般是延续性的，如live, teach, learn, work, study, know.
过去时常用的非持续性动词有come, go, leave, start, die, finish, become, get married等。
举例：
I saw this film yesterday.
（强调看的动作发生过了。）
I have seen this film.
（强调对现在的影响，电影的内容已经知道了。）
Why did you get up so early?
（强调起床的动作已发生过了。）
Who hasn't handed in his paper?
（强调有卷子，可能为不公平竞争。）
She has returned from Paris.
她已从巴黎回来了。
She returned yesterday.
她是昨天回来了。
He has been in the League for three years.
(在团内的状态可延续)
He has been a League member for three years.
(是团员的状态可持续)
He joined the League three years ago.
( 三年前入团，joined为短暂行为。)
I have finished my homework now.

---Will somebody go and get Dr. White?
---He's already been sent for.
句子中如有过去时的时间副词（如 yesterday, last, week, in 1960）时，不能使用现在完成时，要用过去时。
（错）Tom has written a letter to his parents last night.
（对）Tom wrote a letter to his parents last night.

过去完成时

1） 概念：表示过去的过去
----|-------|-----|---->其构成是had +过去分词构成。
那时以前 那时 现在

2） 用法
a. 在told, said, knew, heard, thought等动词后的宾语从句。
She said (that) she had never been to Paris.
b. 状语从句
在过去不同时间发生的两个动作中，发生在先，用过去完成时；发生在后，用一般过去时。
When the police arrived, the thieves had run away.
c. 表示意向的动词，如hope, wish, expect, think, intend, mean, suppose等，用过去完成时表示"原本…，未能…"
We had hoped that you would come, but you didn't.

3) 过去完成时的时间状语before, by, until , when, after, once, as soon as。
He said that he had learned some English before.
By the time he was twelve, Edison had began to make a living by himself.
Tom was disappointed that most of the guests had left when he arrived at the party.

典型例题
The students ___ busily when Miss Brown went to get a book she ___ in the office.
A. had written, left B，were writing, has left C. had written, had left D. were writing, had left
答案D. "把书忘在办公室"发生在"去取书"这一过去的动作之前，因此"忘了书"这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在"同学们正忙于……"这一背景下，when所引导的动作发生。因此
前一句应用过去进行时。

注意： had no … when 还没等…… 就……
had no sooner… than 刚…… 就……
He had no sooner bought the car than he sold it.