现在完成时的概念,希望能讲得通俗一点,

现在完成时（结构：have+过去分词）
(1) 现在完成时表示从过去持续到现在的动作或状态 现在完成时的这种用法通常与由since或for引导的时间状语连用.如：The old man have lived here for more than twenty years.老人已在此住了20多年了.(2) 现在完成时表示过去发生的对现在有影响的动作 [1] 现在完成时的这种用法有时不带时间状语,有时可以和already,before,ever,just,lately,never,once,recently,yet等一些所指时间不具体的时间状语连用.如：Have you ever been to Australia?你去过澳大利亚吗?[2] 有时现在完成时和now,today,this morning,this week,this year等表示现在的时间状语连用.如：I haven' t seen him today.我今天没见过他.I have seen him only once this year.我今年只见过他一次.(3) 现在完成时在时间和条件状语从句中表示将来完成的动作 I'll go to the party as soon as (or when) I have finished my homework.我完成作业后就去参加聚会.(4) 现在完成时和until now,so far,in the past few years,up to the present等表示从某时到目前这段时间的状语连用 I have not heard from her so far.到目前为止,我没有收到过她的信.We have learned five hundred words up to the present.到目前为止,我们已学了五百个生词.但要注意：当意义明确时,适用现在完成时的句子可以不用时间状语.如：He has done a lot of work.他干了许多工作.She has told me about her story.她跟我讲过她的故事.