since引導(dǎo)什么從句表示什么邏輯關(guān)系

　　例句：

　　They've been best mates since school.

　　他們從上學(xué)時(shí)期以來就是最要好的朋友。

　　Things have changed since I was a lad.

　　從我幼時(shí)至今，一切都發(fā)生了變化。

　　She's lived there since before the war.

　　她從戰(zhàn)前起就一直住在那里。