句尾since then的用法

since then意为 "从那时以来"，通常与动词的现在完成时连用，指从过去某一时刻起到现在为止的一段时间。
例句
Have we come far since then?
从那以后．我们取得了很大的进展吗？
He's teach English since then.
从那时起他就教英语。
`Ah, times are greatly changed since then!'
“啊，从那时起，世道可变得多厉害呀！”
Exactly three years have passed since then.
从那时起，整整3年过去了。
Five summers have rolled round since then.
从那时到现在五个夏天已经过去了。