現(xiàn)在完成時(shí)：
表示(1)目前已經(jīng)完成的動(dòng)作,或(2)剛剛完成的動(dòng)作,也可以表示(3)從過去某一刻發(fā)生,現(xiàn)在仍然延續(xù)著的動(dòng)作或情況.這個(gè)時(shí)態(tài)強(qiáng)調(diào)動(dòng)作對(duì)現(xiàn)在的影響.
The conference has lasted for five days.會(huì)議已經(jīng)開了五天.
He has just bought an unusual car.他剛剛買到一輛不一般的小轎車.
當(dāng)句子中出現(xiàn)表示到現(xiàn)在為止這段時(shí)間的狀語時(shí),謂語動(dòng)詞一般用現(xiàn)在完成時(shí):這類狀語有：up to now,up till now,so far,these days,this summer,for 后面接一段時(shí)間的短語或 since 等:
We haven’t seen each other again since we graduated in 1987.1987年畢業(yè)后我們就一直沒見面.
Up till now we have established ten projects.到目前為止我們共上了十個(gè)項(xiàng)目.
So far they have only learned the first three chapters.到現(xiàn)在為止他們只學(xué)了前三章.
We haven’t had much rain this summer.今年夏天沒下多少雨.
一般過去時(shí)：
一般過去時(shí)表示(1)過去某個(gè)特定時(shí)間發(fā)生,并且一下子就完成了的動(dòng)作（即：非持續(xù)性動(dòng)作）,也可以表示(2)過去習(xí)慣性的動(dòng)作.一般過去時(shí)不強(qiáng)調(diào)動(dòng)作對(duì)現(xiàn)在的影響,只說明過去.
I had a word with Julia this morning.今天早晨,我跟朱麗亞說了幾句話.(1)
He smoked many cigarettes a day until he gave up.他沒有戒煙的那陣子,煙抽得可兇了.(2)
一般過去時(shí)常與表示過去的時(shí)間狀語或從句連用,如：yesterday,last week,in 1993,at that time,once,during the war,before,a few days ago,when 等等.
句子中謂語動(dòng)詞是用一般過去時(shí)還是用現(xiàn)在完成時(shí),取決于動(dòng)作是否對(duì)現(xiàn)在有影響.
Have you had your lunch?你吃過午飯了嗎?（意思是說你現(xiàn)在不餓嗎?）
Yes,I have.是的,我已經(jīng)吃過了.（意思是說已經(jīng)吃飽了,不想再吃了.）
When did you have it?你是什么時(shí)候吃的?（關(guān)心的是吃的動(dòng)作發(fā)生在何時(shí).）
I had it about ten minutes ago.我是大約十分鐘以前吃的.
Used to do something 表示過去常做而現(xiàn)在已經(jīng)停止了的習(xí)慣動(dòng)作.
I used to work fourteen hours a day.過去常常一天干十四個(gè)小時(shí).