since引導什么從句表示什么邏輯關系

　　例句：

　　They've been best mates since school.

　　他們從上學時期以來就是最要好的朋友。

　　Things have changed since I was a lad.

　　從我幼時至今，一切都發生了變化。

　　She's lived there since before the war.

　　她從戰前起就一直住在那里。