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.

　?、茉贗t 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。