1） He has been living here since he came to Nanjing 5 years ago. （自从他五年前来到南京，他就一直住在这儿。）

2） They haven't seen each other since last May. （自去年五月起，他们一直没见过面。）

turn在句中做名词，意思是“转折点”。since the turn of the century意思是“自本世纪初（或上世纪末）。”

1） He hasn't written home since the turn of the year. （自去年底以来他还未给家里写过信。）

2） At the turn of the two centuries， they had many hearty wishes for their family.（在两个世纪交替之时，他们对家人有许多衷心的祝愿。）