一课一题一语法：新概念英语第2册第29课
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下面我们继续本周《新概念英语2》第29课的重点句型或语法的分享。先来读一读课文：
一、课文原文
Lesson 29 Taxi!
Captain Ben Fawcett has bought an unusual taxi and has begun a new service. The 'taxi' is a small Swiss aeroplane called a 'Pilatus Porter'. This wonderful plane can carry seven passengers. The most surprising thing about it, however, is that it can land anywhere: on snow, water, or even on a ploughed field. Captain Fawcett's first passenger was a doctor who flew from Birmingham to a lonely village in the Welsh mountains. Since then, Captain Fawcett has flown passengers to many unusual places. Once he landed on the roof of a block of flats and on another occasion, he landed in a deserted car park. Captain Fawcett has just refused a strange request from a businessman. The man wanted to fly to Rockwall, a lonely island in the Atlantic Ocean, but Captain Fawcett did not take him because the trip was too dangerous.
——选自《新概念英语》第二册，外语教学与研究出版社，1997年10月第1版
二、重点句型或语法
本课的重点是一般过去时和现在完成时的用法比较。下面给出两个主要的用法比较供参考。
1. 现在完成时强调对现在的影响和结果，与现在有联系；而一般过去时强调这个动作发生的时间是在过去，不涉及对现在的影响。如：
I have seen this film. （我已经看过了这部电影）
I saw this film yesterday. （我是昨天看的这部电影）
2. 现在完成时常与模糊的时间状语连用（如：for, since, so far, ever, never, just, yet, till/until, up to now, always等）；或者干脆没有时间状语；一般过去时常与具体的时间状语连用（如：yesterday, last night, …ago, in 1980, in February等）。如：
Have you ever been to Spain? (问曾经）
Did you go to Spain last year? （问去年）
三、一课一题
根据上文总结的内容，请选择正确的选项。
When _____ you _____ your computer ?