since then的意思是从那时起，例如Exactly four years have passed since then.从那时起，整整4年过去了。
It was the first in the world.Since then，about one hundred nations have followed that example.这是世界上第一次。从那时起，大约有100个国家效仿了这个例子。
Ever since then I've been longing to meet him .从那以后我一直渴望见到他。
She's teach English since then.
从那时起她就教英语。
