課本中不會(huì)教你的[I]406　It is/has been…since和It was…before

406　It is/has been…since和It was…before

① It is/has been+時(shí)間名詞+since從句表示“自從……以來，多長(zhǎng)時(shí)間了”，主句通常用一般現(xiàn)在時(shí)，since從句用過去時(shí)，表示一個(gè)時(shí)間點(diǎn)。

It is/has been five weeks since I came here. 我來這里已經(jīng)5個(gè)星期了。

提示

上句中的five weeks和twenty years是作為一個(gè)整體看待的，所以用it is。

② It was/had been…since表示“從……時(shí)起，到過去某一時(shí)間止，已有多長(zhǎng)時(shí)間了”。

She said it was/had been thirty years since they married. 她說他們結(jié)婚已有30年了。

③ It was/will be+時(shí)間名詞+before 從句表示“在多長(zhǎng)時(shí)間后才發(fā)生某事”。主句可用過去時(shí)或?qū)頃r(shí)，從句的時(shí)態(tài)要根據(jù)主句的時(shí)態(tài)進(jìn)行變化。

It was three weeks before she received his letter. 3周后她才收到他的信。

It'll be two years before I come here again. 2年后我才會(huì)再來這里。（before 從句中要用一般現(xiàn)在時(shí)表示將來）

④ since 從句中的謂語動(dòng)詞如果是非延續(xù)性的，該動(dòng)詞所表示的動(dòng)作是起點(diǎn)時(shí)間。

It is five months since she left for England. 她去英國已經(jīng)5個(gè)月了。

It was two days since they got there. 他們到達(dá)那里已經(jīng)兩天了。

⑤ since 從句中的謂語動(dòng)詞如果是延續(xù)性的，該動(dòng)詞所表示的動(dòng)作是終止時(shí)間。

It is a year since she lived in the town. 她不住在這個(gè)城里已有1年了。

（=She lived in the town a years ago.）

It was ten years since I taught English. 我不教英語已有10年了。（=I taught English ten years ago.）