It be…since /before /when…从句归纳
“It be…since / before / when…” 结构通常用于表示某个动作或状态从过去某一点时间开始持续到现在，或者在过去某个特定时间点发生。以下是一些例句，以归纳这一结构的用法：
- It has been…since（从过去某一点时间开始到现在）：
- It has been five years since I last saw him.
- 翻译：我上次见到他已经五年了。
这里的结构 “It has been five years since” 表示从过去的某一点时间开始，到现在已经有五年了。
- It has been five years since I last saw him.
- It had been…before（在过去某个特定时间点之前）：
- It had been raining for hours before the sun came out.
- 翻译：太阳出来之前已经下了好几个小时的雨。
“It had been raining for hours before” 表示在过去的某个特定时间点之前，已经下了好几个小时的雨。
- It had been raining for hours before the sun came out.
- It was…when（在过去的某个特定时间点）：
- It was midnight when they finally arrived.
- 翻译：他们终于在半夜到达了。
这个结构 “It was midnight when” 表示在过去的某个特定时间点，即半夜时刻。
- It was midnight when they finally arrived.
这些结构用于描述事件或状态与过去的某一点时间或时间段之间的关系，帮助我们理解时间顺序和持续性。
1. “It be +时间段+since…”表示“自从……以来有多久了”，但若从句谓语是延续性动词时，则意为“(多久) 不做……了”。
2. “It be+时间段+before…”表示“过……之后才……”，若be是否定式，则表示“没过……就……”。
3. “It be +时间点+before…”表示“在……之前，时间是……”。
4. “It be +时间点+when…”表示“当……时，时间是……”。
It is three years since I joined the Party. 我入党有三年了。
It is three years since he lived here. 他不住这里有三年了。
It will be years before we meet again. 要过几年之后我们才能重相聚。
It was not long before he came back. 没过多久他就回来了。
It was evening before they got here. 他们到达这里之前就已天夜了。
It was five o’clock when he got home. 他回到家时已是五点了。(比较强调结构：It was at five o’clock that he got home. )
