2016-2017学年 译林版 必修2 Unit1 tales of the unexplained Grammar 课件 (2)
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Present perfect tense现在完成时

结构:has/have + done We use the present perfect tense when the exact time of an action is not clear or important. We use it with time expressions such as: already(肯定), yet(否定), just, lately, recently, never, ever, for(一段时间), since(时间点)