Present Perfect vs. Past Simple (現在完成式 vs. 過去式)
The main distinction between present perfect and past simple is that one (past simple) states something that happened at a specific point of time in the past and ended in the distant past such as at last December, and the other (present perfect) states something that happened at an unspecific point of time in the past which continues to the present and has not finished yet (specifying duration from the past until now) or may have finished in the recent past with an impact to the present.
1. I have submitted my paper already. (Time of submission is unspecified)
1. I threw my paper away yesterday.
2. I have lived in New York for more than five years. (I still live in New York)
2. I lived in New York for the past two years. (I no longer live in New York)
3. Linda has been ill for over two weeks.
3. Linda was ill two weeks ago.
4. Mary has escaped from prison. <She is still at large>
4. Mary escaped from prison. <She may be captured now>
See details for Present Perfect at http://elisaenglish.pixnet.net/blog/post/2274831
and Past Simple at http://elisaenglish.pixnet.net/blog/post/2633919
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