What were you doing when the UFO arrived?过去进行时的概念及构成构成：主语+was/were+doing sth+时间状语概念：表示过去某一时刻或某段时间正在进行的动作指示词：then、 at that time、once等连用，或者用另一动作 来表示过去的时间。when和while的用法与区别1、延续性动词与非延续性动词延续性动词指动作可以延续一段时间，而不是瞬间 结束。如：work study drink eat 等非延续性动词指动作极为短暂，瞬间结束。如：start begin hit jump knock等When与while引导的时间状语从句When表示”当时候”。主句用过去进行时。从句中既 可以用延续性动词，又可以用非延续性动词，这些动 词既可以表示动作，又可以表示状态。从句中的动作 既可和主句动作同时发生，又可在主句动作之前或之 后发生。 如：Mary was having dinner when I saw her.The boy was still sleeping when his mother got home yesterday evening.When与while引导的时间状语从句lWhile表示“在时候”、“在期间”。从句用过去进行时。它 强调主句的动作与从句的动作同时发生，或主句的动作发生 在从句的动作过程中。While从句必须是表示动作或状态的延 续性动词。如：lThe weather was fine while we were in Beijing.lShe called while I was out.l如果主句的动作在从句的动作过程中发生，从句常用进行时 ，如：lWhile we were swimming someone stole our clotheslDont talk so lould while others are working.Summary1.When可指时间点，又可指时间段，从句中可用延续 性动词，也可用非延续性动词。 2.While总是指一个时间段，从句中必须用延续性动词 。 3.统一时态：主句过去式，从句也是过去式。Exercises: fill with “while” or “when”1. May was talking on the phone,her sister walked in2. Rita bought her new dog,it was wearing a little coat.3. I saw Carlos , he was singing louldly.4. I was dancing , he was singing louldly.5. Linda finally saw David, he was jumping with a dog.6.I was cleaning my room the fire broke out, WhileWhileWhenWhenWhenWhenExercises7. I was walking in the street the accident happened. 8. you have a meeting, you should turn off your mobile phone.9. you have PE class, you should wear sports shoes. 10. I was doing my homework, the phone rang.11. it was raining, the plane took off.12. the teacher was speaking to class, he stood up suddenly.whenWhenWhenWhileWhileWhile谢谢观赏lWhat are dreams? Dreams are one of those things that keep you going and happy.l梦想是什么？ 梦想是让你感到坚持就是幸福的东西。