一般說來，現(xiàn)在完成時(shí)表示過去發(fā)生的動(dòng)作對(duì)現(xiàn)在產(chǎn)生的影響和結(jié)果，著重點(diǎn)在現(xiàn)在。過去完成時(shí)表示過去某一時(shí)間或動(dòng)作之前發(fā)生的另一動(dòng)作或狀態(tài)，即“過去的過去”，必須有一個(gè)具體的過去時(shí)間或動(dòng)作來支撐，強(qiáng)調(diào)對(duì)比。一般過去時(shí)只表示過去發(fā)生了某一動(dòng)作，與現(xiàn)在沒有聯(lián)系，并且有明顯的時(shí)間間隔。

　　例如：

　　1.He had learned more than 5,000 English words when he entered the university at the age of 15?

　　2.Years ago we didn't know this, but recent science has shown that people who don't sleep well soon get ill.

　　3.The policeman's attention was suddenly caught by a small box which had been placed under the Minister's car.

　　4.When the old man started to walk back to his house, the sun had already hidden itself behind the mountain.

　　5.He was hoping to go abroad but his parents have decided that they won’t support him unless he can borrow money from the bank.

　　6.—

　　If the traffic hadn't been so heavy, I could have been back by 6 o'clock.

　　—

　　What a pity! Tina was here to see you.

　　練習(xí)：