如题所述
这是一种不准确的说法。请看下面的例子：
He has already been here for two years. 指到现在为止两年，就用现在完成时。
During the last 30 years, great changes have taken place in our country. 指从现在向前的30年，也就是到现在为为止的30年，因此用现在完成时。
I haven't heard from him since he left last year. 指到现在为止一直没见到他，因此用现在完成时。
再看另外的句子：
I studied English for 4 years. But now I can never speak it any more. 句中for 4 years是指曾经有过4年，隐含着一个过去的时间状语once，或者假设是在上学期间，因此这里只是陈述曾经有过学英语的经历，所以用过去时。
Aunt was too excited to see him return last week. You see, he had never been back since we quarrelled. 句中的since很显然不是表示从那以后到现在的情况，而是到上周他回来的时间为止。追问
He has already been here for two years. 指到现在为止两年，就用现在完成时。
During the last 30 years, great changes have taken place in our country. 指从现在向前的30年，也就是到现在为为止的30年，因此用现在完成时。
I haven't heard from him since he left last year. 指到现在为止一直没见到他，因此用现在完成时。
再看另外的句子：
I studied English for 4 years. But now I can never speak it any more. 句中for 4 years是指曾经有过4年，隐含着一个过去的时间状语once，或者假设是在上学期间，因此这里只是陈述曾经有过学英语的经历，所以用过去时。
Aunt was too excited to see him return last week. You see, he had never been back since we quarrelled. 句中的since很显然不是表示从那以后到现在的情况，而是到上周他回来的时间为止。追问
过去分词就是现在完成时呀
追答完成时态是由助动词have + 过去分词构成的，根据三个时间段可以有
have done 现在完成时
had done 过去完成时
will have done 将来完成时
当然还有与其他时态结合使用的情况。看样子你是初英语的，其他就不必介绍了。我原来解释的对你可能深了点儿。
嗯，我是初二的
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