she looked at me as if i had been a stranger,解释是和现在事实相反的,had been怎么来的,

题目

she looked at me as if i had been a stranger,解释是和现在事实相反的,had been怎么来的,
我知道这句话的意思，但是我的问题在于had been 原型是什么，怎么变来的。thx

答案

as if 是好像的意思,引导的是虚拟语气
主句用一般过去时,从句要后退一个时态,即过去的过去过去完成时