1. since/s?ns/prep.& conj. 自從，自從…以來 +時間點或從句 ，表示動作是什么時候開始得
前面得謂語動詞或主句得謂語動詞必須用完成時，要用延續性動詞。
①since+時間點 介詞
since last week since 2009
I have been here since 2009.
He has stayed here since 5 o’clock.
I have been living here since 2000.
I haven’t heard from him since last summer.
I got a headache since last night.我從昨晚開給就一直頭痛。
They have lived in Beijing since 1980.他們自1980年就一直住在北京。
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②since+ 時間段+ ago
since 5 hours ago
He has stayed here since 5 hours ago.
③since+ 一般過去時得時間狀語從句 連詞
I haven’t seen him since I left that factory.我自從離開那家工廠還沒見過他
We’ve known each other since we were children.我們從小就認識。
I have been here since I graduated in 2000.
She has taught English since he came here.
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since+過去得時間點
=since+一般過去時得句子
=for+時間段
She has lived here for ten years.
=She has lived here since ten years ago. 她已經在這里住了十年了。
I have lived here since two years ago.
=I have lived here for two years.我住在這兒兩年了
I’ve lived here for 15 years.
=I’ve lived here since 15 years ago.
I have been here for 5 years.
=I have been here since 5 years ago.
He has been away since last week.
=He has been away for one week.
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2.既然；因為
Since you agree with me, let’s start together.既然你同意我得觀點，讓我們一起開始吧。
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3.since 也可單獨使用, 自那時起; since前也可加上ever,加強語氣.
I have been here (ever) since.
I have been here (ever) since I graduated in 2000.
It is +一段時間+since+句子(一般過去時)
= 一段時間+has passed +since + 句子(一般過去時)
It is five years since I joined the army.
=Five years has passed since I joined the army.
since then從那以后，句子常用現在完成時，且句中得動詞應用延續性動詞，如果為非延續性動詞必須把它轉換為延續性動詞。
I have not seen him since then.從那以后我沒見過他。
He has written more than 10 books since then.從那以后他寫了十多本書
I haven't heard from her since then.從那以后，我沒有收到地得來信。
We have been good friends since then.從那時起我們就成為好朋友。
