21　during the past three years是什么时态标志

　during the past/last three years 意为“在过去的3年中，近3年来”，也可说成in the past/ last three years。 这个短语指的是到现在为止3年来的状况，是现在完成时的时间标志。

I have been there several times during the past three years . 在过去的3年中我到过那里数次。

During the past month she has read three English books. 她在过去的1个月中读了3本英语书。

He has written three letters to her in the last few weeks . 在过去的几个星期里，他给她写了3封信。