摘要
概念:1.表示过去已经完成的动作对现在产生的影响或造成的结果,常与already,yet,just,before等连用;e.g.We have alteady finished the report;2.表示过去发生动作持续到现在,并可能继续发生下去,常与since和for引导的时间状语连用e.g.I have lived here since I was born;3.谈论从过去到目前为止某个动作发生的次数,常与never,many times,twice等连用e.g.I have already read this book many times.
