怎样区别现在完成时和过去完成时还有过去时,我怎么也区别不了.我明白他们的定义,但是到了题目里我认为是完成时,它是过去时,我认为它是过去时,它又是完成时!

现在完成时用来表示之前已发生或完成的动作或状 态,其结果的确和现在有联系.动作或状态发生在过去 但它的影响现在还存在；也可表示持续到现在的动作或 状态.其构成： have (has) +过去分词.
I have answered the quesion
The quesipn has been solved
Computer has been invited for many years
Have you been to the USA?
He has gone to home