你理解得对.例子：I have been here for an hour.（我到这儿已经有一个小时了.）He has been here for half an hour.（他到这里已经有半个小时了.）I had been out when he came to see me.（他来找我时,我已经出门...knew him last year改为i had been kowing him last year?也可以改为i have known hom since last year?可以改为I have known him since last year. 但不能改为过去完成进行时had been knowing。为什么啊？那除了用have加过去分词的还能怎么做啊？过去完成进行时极少用到，在这里不适宜用，合适的例子一时难以找到。除了have known，还可以变为：I knew him a year ago. 或者 I got to know him last year. 或者 I got to know him a year ago. 或者 I have known him for a year.i knew him last year改写为现在完成进行时态怎么改？这样改：I have been knowing him since last year. （自从去年起，我就认识他。）