怎样区分现在完成时和一般过去时

一般过去时有两种形式 1,was,were做谓语 2,实意动词过去式做谓语 I was so tired. I closed the door. 现在完成时也是两种 1,has/have been做谓语 2,has/have+动词过去分词做谓语 而且一般有个持续的时间段做状语。 I have been Like this for three years. I have finished my work.