一、时态讲解：现在完成时（1）构成：现在完成时由助动词 have + 过去分词构成，助动词 have 有人称和数的变化。第三人称单数用 has，其余用 have.现在完成时的否定式直接在助动词后面加上 not、疑问式是把助动词提到主语之前。以study 为例，其否定式、疑问式和简单回答形式如下：否定式疑问式I have not (haven’t) studied….Have I studied…?You have not (haven’t) studied….Have you studied…?He has not (hasn’t) studied….Has he studied…?否定疑问式简单回答（肯定/否定）Have I not (Haven’t I) studied…?Yes, you have. No, you haven’t.Have you not (Haven’t you) studied…?Yes, I have. No, I haven’t.Has he not (Hasn’t he) studied…?Yes, he has. No, he hasn’t.（2）用法：1）现在完成时通常表示在说话之前已经完成的动作或存在的状态。说话人强调的是该动作或状态对现在的结果或影响。 My daughter has just gone out. 我女儿刚出去。 I’m sure we’ve met before. 我肯定我们以前见过面。 She has arrived. 她到了。2）表示持续到现在的动作或状态，往往和包括现在在内的表示一段时间的状语连用，如recently, already, just, lately, for…, since…,yet 等。如： I haven’t heard from her these days. 这些日子我没有收到她的信。 We haven’t seen you recently. 最近我们没有见到你。 They have been away for two years. 他们离开已经两年了。She has been with us since Monday.★注意：a)since 和 for 的区别since 后接时间点，如 1993，last term, yesterday, the time I got therefor 后接一段时间，表示“长达多久”，如 ten years, a while, two days 等。Exercise: 用 since 和 for 填空1. Jim has been in Ireland ______ Monday.2. Jill has been in Ireland ______ three days.3. His aunt has lived in Australia ______15 days.4. Mary is in her office. She has been there ______ 7 o'clock.5. India has been an independent country ______1974.6. The bus is late. They've been waiting ______ 20 minutes.7. Nobody lives in those houses. They have been empty ______...
