楼主没有提供变化格式,至少有以下几种：
Mrs Black has been here for two years.
= Mrs Black came here two years ago.
= Mrs Black has been here (ever) since two years ago.
= Mrs Black has been here as long as two years.
= It is two years since Mrs Black came here.
= It has been two years since Mrs Black came here.
= Two years has passed since Mrs Black came here.