大神求讲解虚拟语气

she is very kind to me as if she were my sister
我 在说这句话的时候是强调现在，从 is 可以体现，
虚拟语气推前一个时态：现在 +过去 =过去
若用had been的话应该是 she was very kind to me as if she had been my sister
是 过去 + 过去 = 过去完成时

虚拟分主从，清纯时间观念

虚拟分主从，清楚时间观念