1. It's + some time + since從句.
翻譯：“自從...以來(lái)已經(jīng)多久了”.
要求：since從句的時(shí)態(tài)必須是一般過(guò)去時(shí).
如：It's ten years since I graduated.
自從我畢業(yè)以來(lái),已經(jīng)十年了.
2. It's + some time + that從句.
翻譯：“...多久了”.
要求：此為強(qiáng)調(diào)句型,去掉It's和that之后,剩下部分必須是個(gè)完整的句子.
如：It's ten years that I've lived here for.
還原成：I've lived here for ten years.
我在這兒居住已經(jīng)長(zhǎng)達(dá)十年了.
3. It's + sometime + when從句.
翻譯：“...是在某個(gè)時(shí)刻”.
要求：when從句是定語(yǔ)從句,要求從句的時(shí)態(tài)和It's的is/was對(duì)應(yīng).
如：It was ten years ago when I graduated.
我畢業(yè)是在十年前.
4. It's + some time + before從句.
翻譯：“過(guò)了多久...才...”.
要求：before從句的時(shí)態(tài)必須是一般過(guò)去時(shí)；It's = It was.
如：It's ten years before I graduated.
過(guò)了十年后,我才畢業(yè).