4. 在it is+時(shí)間+since從句結(jié)構(gòu)中，since從句是非延續(xù)性動(dòng)詞的一般過(guò)去時(shí)，含有肯定意味。

　　例如：

　　It is three years since her husband left her.

　　她丈夫離開(kāi)她已經(jīng)3年了。

　　It is over sixty years since the People’s Republic of China was established.

　　中華人民共和國(guó)已經(jīng)成立60多年了。

　　5. 在it is+時(shí)間+since從句結(jié)構(gòu)中，since從句是延續(xù)性動(dòng)詞的一般過(guò)去時(shí)，含有否定的意味。

　　例如：

　　It is three years since she stayed here.

　　她離開(kāi)這里已經(jīng)3年了。

　　How long is it since you were a league member?

　　你退團(tuán)有多久了?

　　6. 在it is+時(shí)間+since從句結(jié)構(gòu)中，since從句是現(xiàn)在完成時(shí)或過(guò)去完成時(shí)，均含有否定意味。

　　例如：

　　It is five years since we have seen her.

　　我們已經(jīng)5年沒(méi)有見(jiàn)她了。

　　It was years since I had seen her.

　　在那之前，我已經(jīng)有好久沒(méi)有見(jiàn)到她了。

　　It’s been a long time since I’ve seen you.

　　我已經(jīng)很久沒(méi)有見(jiàn)到你了。

　　另外，①根據(jù)英語(yǔ)慣用法，since從句不可以否定形式出現(xiàn)。

　　例如：

　　It is four years since I have smoked a cigarette. 我已經(jīng)4年不抽煙了。

　　不可說(shuō)：It is four years since I haven’t smoked a cigarette.

　　但由于下句中的since不作“自從”解，所以從句可以用否定形式。

　　例如：

　　I haven’t been out anywhere since I don’t know how long.

　　也不知多久了，我哪兒也沒(méi)去過(guò)。

　?、赟ince從句通常不與非延續(xù)性動(dòng)詞的現(xiàn)在完成時(shí)的肯定式連用。

　　例如：

　　Her mother died when she was a child.

　　她小時(shí)候母親就去世了。

　　不可說(shuō)：Her mother has died since she was a child.

　　③Since前不可加表示時(shí)間的詞語(yǔ)，但可以與ago連用。

　　例如：

　　She has lived with us since her mother died three years ago.

　　自從她母親3年前去世，她就一直和我們住在一起。

　　不可說(shuō)：She has lived with us three years since her mother died.

　　④在It was five years ago since his father died. 一句中的since用錯(cuò)了，因?yàn)樵诤衋go的時(shí)間范疇里，已經(jīng)有了從過(guò)去的一個(gè)時(shí)間點(diǎn)以來(lái)的時(shí)間，即已有了since的時(shí)間范疇，所以再用since是多余的。

　　改為：

　　It was five years ago that his father died.

　　他父親5年前去世了。

　　It is five years since his father died.

　　他父親去世已經(jīng)5年了。