今天我们一起学习英语基础语法中12种时态中的过去完成时。
过去完成时是一个相当容易理解和使用的一个时态。这个时态谈论的是“过去的事”（ "past in the past"）
我们如何使用过去完成时呢？
过去完成时的结构是：
1、混淆助动词(have)在一般过去时中会变成:had
The auxilary verb (have) is conjugated in the Past Simple: had
2、主要动词在过去分词中是不变的，只是后面加了一个 -ed（或者不规则的）
The main verb is invariable in past participle form: -ed (or irregular)
3、对于否定句，我们在助动词和主动词之间加not。
4、对于疑问句，我们交换主语和助动词。
请看以下带有过去完成时的栗子：
与过去完成时连用的缩略语
当我们在说话中使用过去完成时的时候，经常收缩主语和助动词。有时候我们也会以非正式的书面形式这样做：
When we use the Past Perfect in speaking, we often contract the subject and the auxiliary verb. We also sometimes do this in informal writing:
举个栗子：
I'd eaten already.
They'd gone home.在否定句中，我们缩写助动词和“not”：
I hadn't finished my meal.
Anthony hadn't had a day off for months.
我们该如何使用过去完成时呢？
过去完成时表示的动作在过去的另一个动作之前。这都是过去的事了。举个例子：
The train left at 9am. We arrived at 9: 15am. When we arrived, the train had left.
I wasn't hungry. I had just eaten.
They were hungry. They had not eaten for five hours.
I didn't know who he was. I had never seen him before.
"Mary wasn't at home when I arrived." / "Really? Where had she gone?"
你可以把过去完成时想象成现在完成时，但时间不是现在，而是之前。
You can sometimes think of the Past Perfect tense like the Present Perfect tense, but instead of the time being now the time is before.
举个栗子：
假设你在9:15到达车站，站长对你说：
"You are too late. The train has left."
稍后，你告诉你的朋友们：
"We were too late. The train had left."
我们经常在转述的言语中使用过去完成时，跟在动词后面，比如：said, told, asked, thought, wondered
请看下面栗子：
He told us that the train had left.
I thought I had met her before, but I was wrong.
He explained that he had closed the window because of the rain.
I wondered if I had been there before.
I asked them why they had not finished.
今天分享到此为止，接下来将继续学习并分享更多关于英语时态的学习知识，
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