I have been here since I was born 和I haden't seen him since he left NANJING.两句话为什么用的不是相同的时态?

i have been here many a I HAVE BEEN HERE SINCE TIME o,i have been here before是什么意思 i have never been here还是i have never been in here I have been here 与I have been living here一样吗?有点弄不清楚. I have been here before.Is this correct?我曾经在这里.1）I have been here before.2）I have been here. I have lived here since then还是I have been here since then对啊? I have already been here for 5years =I have been here_____5 years______ I have been here to meet you again I have been here ( )1980要填什么 I have been to you here这句话是什么意思 I have been here for three months.同义句 i have been here ( )a year.A,since B,for i have been here for three months同义句 I have been here since three yeas ago 请问“I shouldn't have been here.”怎么翻译? I have been working here for 7 years.改为同义句怎摸说形如I have been working here— — — i have know him since i have been here.为什么不成立