1) since +過(guò)去一個(gè)時(shí)間點(diǎn)(如具體的年、月、日期、鐘點(diǎn)、1980, last month, half past six)。

I have been here since 1989.

2) since +一段時(shí)間+ ago

I have been here since five months ago.

3) since +從句

Great changes have taken place since you left.

Considerable time has elapsed since we have been here.

4) It is +一段時(shí)間+ since從句

It is two years since I became a postgraduate student.

相關(guān)內(nèi)容：

不用進(jìn)行時(shí)的動(dòng)詞

語(yǔ)法講解：疑問(wèn)代詞

need 不必做和本不該做

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