结构:主语 + have/has + 过去分词二、现在完成时的基本用法: 1.表示动作在说话时已经完成,但对现在产生某种影响。 e.g.:i have had breakfast and i am full now. she has read the book and she knows something about it. 2.表示动作发生在过去,一直持续到现在,可能还会继续进行下去。(动词一般是延续性动词) e.g.: they have lived here for 2 years. tom has taught in this school till now.